Suzuki–Miyaura coupling of phosphinoyl-α-allenic alcohols with arylboronic acids catalyzed by a palladium complex “on water”: an efficient method to generate phosphinoyl 1,3-butadienes and derivatives

Abstract

We report here the first palladium-catalyzed Suzuki–Miyaura couplings of phosphinoyl-α-allenic alcohols with arylboronic acids “on water” without phase-transfer catalysts or additives. This new methodology provides a novel approach to generate phosphinoyl 1,3-butadienes and derivatives with medium to excellent yields. A mechanism via initial C(sp³)–OH bond cleavage of the substrate to form π-allyl-palladium intermediates, and transmetallation with arylboronic acid, followed by reductive elimination to afford the product, is proposed.

---

Introduction

Suzuki–Miyaura cross-coupling¹ catalyzed by transition metals is one of the most versatile approaches for constructing biaryl and alkene derivatives towards key moieties of numerous natural products, agrochemicals, pharmaceuticals, and functional polymers etc. Current achievements of the Suzuki–Miyaura coupling have been carried out chiefly by using different ligands and/or metals,^1b,2 various reaction media.³ Noticeable advances have been achieved with conducting reactions in water or aqueous solution. From environmental and economic points of view, water as cheap, readily available, non-toxic and non-flammable solvent has been one of the most important choices for organic transformations in green chemistry. In this respect, a number of remarkable results reported by the groups of Glorius, Beller, Herrman, Nolan, Organ and Köhler etc. have been documented conducting the cross-coupling of boronic derivatives with aryl halides in water.^2a,4 In order to improve the catalytic efficiency, efforts are also focused on changing the property of organoboronic compounds.^1a However, less attention has been paid on exploring novel substrates except conventional electrophiles including alkyl, aryl, alkenyl and alkynyl groups. Currently, alternative allylic partners⁵ possessing electron-deficient bonds, such as acetates, carbonates, halides and pseudohalides, are emerging into hot topic research. Moreover, the allylic/allenic substrates with electron-rich functionality such as C–OR, C–OH are still particularly attractive and challenging.⁶ In 2009, Lipshutz et al. disclosed the first Suzuki–Miyaura couplings of functionalized allylic ethers with arylboronic acids in water at room temperature with the presence of phase-transfer catalyst (nonionic amphiphilic PTS).^6a Parallel experiments shown the coupling reaction “on water” proceeded sluggishly which further demonstrated the key role of phase-transfer catalyst PTS. On the other hand, the use of allylic alcohols or α-allenic alcohols as electrophiles for Suzuki–Miyaura coupling is more attractive with respect to atom-economy, albeit limited examples have been reported in refluxing organic solvents [Scheme 1a and b].^6e,f,8a–e It is noteworthy that the above processes went through π-allyl-palladium intermediates for all of the allylic fragments, no exception to most of the allenic fragments.⁷ Interestingly, to the best of our knowledge, the coupling reaction of phosphinoyl-α-allenic alcohols with arylboronic acids “on water” has not been reported to date⁸ [Scheme 1c].

Scheme 1 (a) Palladium catalyzed cross-couplings of allylic alcohols with arylboronic acids; (b) palladium catalyzed coupling of α-allenic alcohols with arylboronic acids (hydroarylation pathway); (c) this work. (d) Han's first catalytic methods to generate phosphinoyl 1,3-butadienes.

Organophosphorus compounds play key roles in catalysis, organic synthesis, biochemistry and materials chemistry, which necessitate their significance in preparation.⁹ Phosphinoyl 1,3-dienes as one of the functionalized phosphorous compounds are readily be transformed to other valuable compounds, including allylic phosphonates,¹⁰ Diels–Alder cyclization products,¹¹ cyclohexa-dienylphosphonates,¹² vinyl allenes¹³ and phosphine-functionalized copolymers¹⁴ etc. However, to be noted, the conventional methods for synthesizing phosphinoyl 1,3-dienes are problematic and quite limited. Until recently, Han et al. reported the first nickel-catalyzed generation of phosphinoyl 1,3-butadienes [Scheme 1d], consisting of the metal-catalyzed addition of diphenylphosphine oxide and related P(O)H compounds to propargyl alcohols followed by an acid-catalyzed dehydration.¹⁵ Although this method provides quite convenient approach to phosphinoyl 1,3-butadienes, only terminal alkynes can be used, moreover, the adducts suffered from mixtures of Markovnikov and anti-Markovnikov products. Thus, the potential development with diversity and high selectivity/efficiency is highly demanded. In continuing research on synthesis and application of organophosphorus chemistry,¹⁶ herein we report, for the first time, palladium-catalyzed Suzuki–Miyaura couplings of phosphinoyl-α-allenic alcohols with arylboronic acids “on water” to generate phosphinoyl 1,3-butadienes and derivatives [Scheme 1c].

Results and discussions

Initially, a number of metal sources and ligands/additives along with solvents were examined for the cross-coupling of phosphinoyl-α-allenic alcohols (1a) with p-methoxylphenyl-boronic acid (2a) under refluxing temperature (Table 1). Nickel and copper catalysts exhibited no activity to this type of couplings (entries 1, 2, 6). Rhodium,^8f,17 platinum^8b and palladium sources were proven to be superior to afford medium yields in neat water, thus we extensively screened palladium precursors including PdCl₂, Pd(OAc)₂, Pd(TFA)₂, (Ph₃P)₄Pd and Pd/C. Although phase-transfer catalyst/surfactants were widely used for accelerating Suzuki–Miyaura couplings in water,^4l,18 TOABr (Tetraoctylammonium Bromide) and PEG 2000 were shown no improvements, instead of furnishing lower yields (entries 15, 16). Similarly, the presence of organic solvents and bases didn't increase the efficiency. Gratifyingly, the yield was significantly affected by the nature of the ligand and the palladium source. Phosphine ligands were revealed much higher activities than nitrogen ligands such as 1,10-phenanthroline and 2,2′-bipyridine (entries 17, 18). To be noted, mono-dentate phosphine ligands underwent smoother transmetallation with arylboronic acids than bidentate phosphine ligands since the latter tended to form coordinatively saturated π-allyl-palladium intermediates towards slower transmetallation, which has been demonstrated by Lipshutz et al.^6a Eventually, bis(triphenyl-phosphine)palladium chloride was found to be the best catalyst to facilitate the coupling of 1a and 2a “on water” under refluxing temperature without phase-transfer catalysts or additives, affording the adduct (3a) with 84% yield (entry 21).

Table 1 Reaction condition optimizations: metal-catalyzed coupling of phosphinoyl-α-allenic alcohol and p-methoxyl phenylboronic acid^a

Entry	Catalyst	Solvent/additive/base	Yield^b (%)
a 1 mmol phosphinoyl-α-allenic alcohol, 2 mmol p-methoxyl phenylboronic acid, 10 mL solvent, 5 mol% catalyst, refluxed for 2 h.b Isolated yield based on allenes.c Reaction under room temperature for 24 h.
1	Ni(OTf)2	H2O	0
2	Ni(PPh3)2Cl2	H2O	0
3	(PPh3)3RhCl	H2O	45
4	Rh2(OAc)2	H2O	40
5	PtCl2	H2O	42
6	CuI	H2O	0
7	PdCl2	H2O	45
8	Pd/C (10%)	H2O	0
9	(Ph3P)4Pd	H2O	23
10	Pd(TFA)2	H2O	35
11	Pd(OAc)2	H2O	46
12	Pd(OAc)2	H2O/K2CO3	46
13	Pd(OAc)2	H2O/KOH	45
14	Pd(OAc)2	H2O : dioxane = 9 : 1/K2CO3	30
15	Pd(OAc)2	H2O/TOABr/K2CO3	30
16	Pd(OAc)2	H2O : PEG 2000 = 3 : 3.5	29
17	Pd(OAc)2/1,10-phenanthroline	H2O	Trace
18	Pd(OAc)2/Bipy	H2O	Trace
19	Pd(OAc)2(DPPE)	H2O	Trace
20	Pd(TFA)2(DPPE)	H2O	58
21	Pd(PPh3)2Cl2	H2O	84
22	Pd(PPh3)2Cl2	H2O : THF = 9 : 1	59
23	(BINAP)PdCl2	H2O	56
24	(Xantphos)PdCl2	H2O	54
25	Pd(PPh3)2Cl2	H2O	0^c

---

The optimized conditions from the data in Table 1 (5 mol% Pd(PPh₃)₂Cl₂, refluxing water) were generally applicable to several phosphinoyl-α-allenic alcohols and arylboronic acids (Table 2). The coupling of phosphinoyl-α-allenic alcohols (1a) with arylboronic acids bearing electron-rich or electron–neutral groups were effective to afford phosphinoyl 1,3-butadienes with medium to excellent yields (entries 1–5). However, arylboronic acids with electron-deficient groups, including –Br, –F and –NO₂, led to decrease of coupling yields dramatically even after longer reaction time (entries, 6–8). This phenomenon might be attributed to the easier polymerization of electron-deficient conjugated dienes especially under heterogeneous high concentration, indicated by the isolation of oligmers. With respect to substituents on phosphinoylallenes, the substrates with groups ranged from alkyl to aromatic, electron-rich to electron-deficient (entries 9–22) were shown medium to excellent yields of phosphinoyl 1,3-butadiene derivatives. For unsymmetrical phosphinolyallenes 1e, 1h, the couplings gave exclusively E-isomers of 3o, 3p and 3u, respectively. This improved selectivity can be explained by relative differences in the stabilities and reactivities of intermediates affected by the electron-deficient groups on allenes. Notably, substrates with high steric substituents did not impair the catalytic efficiency, remaining yield up to 94% (entries 19–22). It is worth to mention that all of these substrates afforded comparable yields with terminal phosphinoylallenes (1a) even in the case of coupling with electron-deficient arylboronic acids (entries 14, 16, 22).

Table 2 The palladium-catalyzed couplings of substituted phosphinoyl-α-allenic alcohols with various arylboronic acids^a

Entry	R^1	R^2	R^3	Yield^b of 3
a 1 mmol phosphinoyl-α-allenic alcohol, 2 mmol arylboronic acid, 10 mL solvent, reflux.b Isolated yield based on allenes.c E : Z ratios and relative stereochemistries were determined by ^31P-NMR and NOESY experiments, respectively.
1	H	H (1a)	p-MeO	84 (3a)
2	H	H (1a)	p-Me	82 (3b)
3	H	H (1a)	o-Me	96 (3c)
4	H	H (1a)	H	61 (3d)
5	H	H (1a)	Naphthalene	60 (3e)
6	H	H (1a)	p-Br	44 (3f)
7	H	H (1a)	p-F	25 (3g)
8	H	H (1a)	m-NO2	25 (3h)
9	CH3	CH3 (1b)	p-MeO	78 (3i)
10	CH3	CH3 (1b)	H	61 (3j)
11	–C5H10– (1c)		o-Me	90 (3k)
12	–C5H10– (1c)		H	73 (3l)
13	p-MeOC6H4	H (1d)	H	69 (3m) [2.9 : 1]^c
14	p-MeOC6H4	H (1d)	p-Br	52 (3n) [7.1 : 1]^c
15	p-CF3C6H4	CH3 (1e)	H	85 (3o) [Only E]^c
16	p-CF3C6H4	CH3 (1e)	p-F	84 (3p) [Only E]^c
17	CH3CH2	H (1f)	H	73 (3q) [12 : 1]^c
18	CH3CH2	H (1f)	p-Me	95 (3r) [12.3 : 1]^c
19	Ph	Ph (1g)	p-MeO	92 (3s)
20	Ph	Ph (1g)	H	94 (3t)
21	CH3CH2	p-ClC6H4 (1h)	H	72 (3u) [Only E]^c
22	CH3CH2	p-ClC6H4 (1h)	m-NO2	60 (3v) [2.3 : 1]^c

---

Although the mechanism of this reaction is still under exploration, we proposed a catalytic cycle based on the preliminary results and previous studies^6e,f,19 for the cross-coupling of phosphinoyl-α-allenic alcohol with arylboronic acids “on water” (Scheme 2).²⁰ Firstly, the hydroxy group and C=C bond of phosphinoyl-α-allenyl alcohol 1 is activated by arylboronic acids 2 and in situ formed palladium(0) species, respectively. Subsequently, cleavage of allenic carbon–oxygen bond leads to form π-allyl-palladium species 5, which undergoes transmetallation with arylboronic acids to give intermediates 6 and 6′. No observation of product 7 indicates the priority of forming intermediate 6. Eventually, reductive elimination of 6 affords the final phosphinoyl 1,3-butadienes 3 and concurrently regenerates palladium(0) species.

Scheme 2 Plausible mechamism for palladium-catalyzed Suzuki–Miyaura coupling of phosphinoyl-α-allenic alcohol with arylboronic acids on water.

Conclusions

In conclusion, we have developed a novel palladium-catalyzed Suzuki–Miyaura coupling of phosphinoyl-α-allenic alcohols with arylboronic acids “on water” without surfactants or additives. In the presence of 5 mol% Pd(PPh₃)₂Cl₂, varieties of phosphinoyl-α-allenic alcohols smoothly coupled with arylboronic acids to afford phosphinoyl 1,3-butadienes and derivatives in medium to excellent yields. This work suggests a new transformation of allenes to phosphinoyl multi-substituted conjugated dienes. Further application of this methodology with tandem reactions to build bioactive compounds is under way.

Experimental

To a 10 mL flask equipped with condenser under nitrogen was added phosphinoyl-α-allenic alcohol (1 mmol), arylboronic acid (2 mmol), Pd(PPh₃)₂Cl₂ (5 mol%), and 10 mL degassed water. The reaction mixture was then heated to reflux for several hours until the complete consuming of starting materials monitored by TLC. After being cooling down, the reaction was extracted with ethyl acetate (5 mL × 2). The crude product was purified on flash chromatography, with ethyl acetate/petroleum ether (1 : 1) as eluents to afford product.

Acknowledgements

This project is supported by the National Natural Science Foundation of China (no. 21002019), the Foundation Research Project of Jiangsu Province (The Natural Science Found no. BK20141359), the Fundamental Research Funds for the Central Universities (NJAU, no. KYRC201211) and “QinLan Project” of JiangSu Province.

Notes and references

1. (a) A. J. J. Lennox and G. C. LIoyd-Jones, Chem. Soc. Rev., 2014, 43, 412; (b) F.-S. Han, Chem. Soc. Rev., 2013, 42, 5270; (c) N. Kambe, T. Iwasaki and J. Terao, Chem. Soc. Rev., 2011, 40, 4937; (d) C. M. So and F. Y. Kwong, Chem. Soc. Rev., 2011, 40, 4963; (e) G. C. Fu, Acc. Chem. Res., 2008, 41, 1555; (f) R. Martin and S. L. Buchwald, Acc. Chem. Res., 2008, 41, 1461; (g) N. Miyaura, in Metal-Catalyzed Cross-Coupling Reactions, ed. A. de Meijere and F. Diederich, Wiley-VCH, New York, 2004, ch. 2; (h) A. Suzuki, in Handbook of Organopalladium Chemistry for Organic Synthesis, ed. E. Negishi, Wiley-Interscience, New York, 2002, ch. 3, Pt. 2.2; (i) S. Kotha, K. Lahiri and D. Kashinath, Tetrahedron, 2002, 58, 9633; (j) N. Miyaura and A. Suzuki, Chem. Rev., 1995, 95, 2457; (k) T. Moriya, T. Furuuchi, N. Miyaura and A. Suzuki, Tetrahedron, 1994, 50, 7961.
2. (a) C. Valente, S. Çalimsiz, K. H. Hoi, D. Mallik, M. Sayah and M. G. Organ, Angew. Chem., Int. Ed., 2012, 51, 3314; (b) T. M. Shaikh, C.-M. Weng and F.-E. Hong, Coord. Chem. Rev., 2012, 256, 771; (c) B. M. Rosen, K. W. Quasdorf, D. A. Wilson, N. Zhang, A.-M. Resmerita, N. K. Garg and V. Percec, Chem. Rev., 2011, 111, 1346; (d) R. Jana, T. P. Pathak and M. S. Sigman, Chem. Rev., 2011, 111, 1417.
3. For selected Suzuki–Miyaura coupling in neat water, aqueous solution, PEG, ionic liquids and supercritical carbon dioxide, see: (a) F. Rajabi and W. R. Thiel, Adv. Synth. Catal., 2014, 356, 1873; (b) G.-F. Zhang, Y.-X. Luan, X.-W. Han, Y. Wang, X. Wen, C.-R. Ding and J.-R. Gao, Green Chem., 2013, 15, 2081; (c) V. Polshettiwar, A. Decottignies, C. Len and A. Fihri, ChemSusChem, 2010, 3, 502; (d) A. D. Silva, J. D. Senra, L. C. S. Aguiar, A. B. C. Simas, A. L. F. de Souza, L. F. B. Malta and O. A. C. Antunes, Tetrahedron Lett., 2010, 51, 3883; (e) T. M. Razler, Y. Hsiao, F. Qian, R. L. Fu, R. K. Khan and W. Doubleday, J. Org. Chem., 2009, 74, 1381; (f) L.-Y. Li, J.-Y. Wang, T. Wu and R.-H. Wang, Chem.–Eur. J., 2012, 18, 7842; (g) R. R. Fernandes, J. Lasri, M. F. C. G. da Silva, A. M. F. Palavra, J. A. L. da Silva, J. J. R. F. da Silva and A. J. L. Pombeiro, Adv. Synth. Catal., 2011, 353, 1153.
4. Glorius: (a) G. Altenhoff, R. Goddard, C. W. Lehmann and F. Glorius, J. Am. Chem. Soc., 2004, 126, 15195 ; Beller:; (b) S. Harkal, F. Rataboul, A. Zapf, C. Fuhrmann, T. Riermeier, A. Monsees and M. Beller, Adv. Synth. Catal., 2004, 346, 1742; (c) A. Zapf and M. Beller, Chem.–Eur. J., 2004, 10, 1830; (d) A. Zapf, A. Ehrentraut and M. Beller, Angew. Chem., Int. Ed., 2000, 39, 4153 ; Herrmann:; (e) C. W. K. Gstöttmayr, V. P. W. Böhm, E. Herdtweck, M. Grosche and W. A. Herrmann, Angew. Chem., Int. Ed., 2002, 41, 1363–1365; (f) S. K. Schneider, P. Roembke, G. R. Julius, H. G. Raubenheimer and W. A. Herrmann, Adv. Synth. Catal., 2006, 348, 1862–1873 ; Nolan:; (g) N. Marion, O. Navarro, J.-G. Mei, E. D. Stevens, N. M. Scott and S. P. Nolan, J. Am. Chem. Soc., 2006, 128, 4101; (h) S. D. González, N. Marion and S. P. Nolan, Chem. Rev., 2009, 109, 3612; (i) O. Diebolt, V. Jurcík, R. Correa da Costa, P. Braunstein, L. Cavallo, S. P. Nolan, A. M. Z. Slawin and C. S. J. Cazin, Organometallics, 2010, 29, 1443; (j) C. Zhang, J. Huang, M. L. Trudell and S. P. Nolan, J. Org. Chem., 1999, 64, 3804 ; Organ:; (k) E. A. B. Kantchev, C. J. O’Brien and M. G. Organ, Angew. Chem., Int. Ed., 2007, 46, 2768 ; Köhler:; (l) C. Röhlich, A. S. Wirth and K. Köhler, Chem.–Eur. J., 2012, 18, 15485; (m) S. S. Soomro, C. Röhlich and K. Köhler, Adv. Synth. Catal., 2011, 353, 767; (n) C. Röhlich and K. Köhler, Adv. Synth. Catal., 2010, 352, 2263.
5. Selected examples for coupling of allylic fragments: (a) C. Nájera, J. Gil-Moltó and S. Karlström, Adv. Synth. Catal., 2004, 346, 1798; (b) G. W. Kabalka and M. Al-Masum, Org. Lett., 2006, 8, 11; (c) G. W. Kabalka, E. Dadush and M. Al-Masum, Tetrahedron Lett., 2006, 47, 7459; (d) H. Tsukamoto, T. Uchiyama, T. Suzuki and Y. Kondo, Org. Biomol. Chem., 2008, 6, 3005; (e) R. Matsubara and T. F. Jamison, J. Am. Chem. Soc., 2010, 132, 6880; (f) H. Ohmiya, N. Yokokawa and M. Sawamura, Org. Lett., 2010, 12, 2438; (g) H. Ohmiya, Y. Makida, D. Li, M. Tanabe and M. Sawamura, J. Am. Chem. Soc., 2010, 132, 879; (h) C.-G. Li, J.-X. Xing, J.-M. Zhao, P. Huynh, W.-B. Zhang, P.-K. Jiang and Y. J. Zhang, Org. Lett., 2012, 14, 390; (i) J. M. Zhao, J. Ye and Y. J. Zhang, Adv. Synth. Catal., 2013, 355, 491.
6. (a) T. Nishikata and B. H. Lipshutz, J. Am. Chem. Soc., 2009, 131, 12103; (b) T. Mino, T. Kogure, T. Abe, T. Koizumi, T. Fujita and M. Sakamoto, Eur. J. Org. Chem., 2013, 1501; (c) J. K. Park, H. H. Lackey, B. A. Ondrusek and D. T. McQuade, J. Am. Chem. Soc., 2011, 133, 2410; (d) S. Asako, L. llies and E. Nakamura, J. Am. Chem. Soc., 2013, 135, 17755; (e) H.-B. Wu, X.-T. Ma and S.-K. Tian, Chem. Commun., 2014, 50, 219; (f) H. Tsukamoto, T. Uchiyama, T. Suzuki and Y. Kondo, Org. Biomol. Chem., 2008, 6, 3005; (g) J. Ye, J. M. Zhao, J. Xu, Y. X. Mao and Y. J. Zhang, Chem. Commun., 2013, 49, 9761.
7. For employing α-allenic esters, phosphates or alcohols as initial π-allyl-palladium precursors (cleavage of C–OR, C–OH bonds by palladium complexes), see: (a) D. Djahanbini, B. Cazes and J. Gore, Tetrahedron Lett., 1984, 25, 203; (b) J. Nokami, A. Maihara and J. Tsuji, Tetrahedron Lett., 1990, 31, 5629; (c) Z. Ni and A. Padwa, Synlett, 1992, 869; (d) W. Li and M. Shi, J. Org. Chem., 2008, 73, 6698 . In some cases, α-allenic alcohols are depicted undergo hydroarylation pathway before forming π-allyl-palladium intermediates, see ref. 8b–d.
8. Transition metal-catalyzed additions of arylboronic acids to α-allenic alcohols in organic solvents are rare. Palladium: (a) M. Yoshida, T. Gotou and M. Ihara, Chem. Commun., 2004, 1124; (b) M. Yoshida, K. Matsuda, Y. Shoji, T. Gotou, M. Ihara and K. Shishido, Org. Lett., 2008, 10, 5183; (c) M. Yoshida, Y. Shoji and K. Shishido, Org. Lett., 2009, 11, 1441; (d) M. Yoshida, Y. Shoji and K. Shishido, Tetrahedron, 2010, 66, 5053; (e) M. Yoshida, T. Kasai, T. Mizuguchi and K. Namba, Synlett, 2014, 25, 1160 ; rhodium:; (f) T. Miura, H. Shimizu, T. Igarashi and M. Murakami, Org. Biomol. Chem., 2010, 8, 4074.
9. (a) L. D. Quin, A Guide to Organophosphorus Chemistry, Wiley-Interscience, New York, 2000; (b) K. V. L. Crepy and T. Imamoto, Top. Curr. Chem., 2003, 229, 111; (c) C. S. Demmer, N. Krogsgaard-Larsen and L. Bunch, Chem. Rev., 2011, 111, 7981.
10. S. D. Darling, F. N. Muralidharan and V. B. Muralidharan, Tetrahedron Lett., 1979, 20, 2761.
11. (a) C. E. Griffin and W. M. Daniewski, J. Org. Chem., 1970, 35, 1691; (b) E. Villemin, K. Robeyns, R. Robiette, M.-F. Herent and J. Marchand-Brynaert, Tetrahedron, 2013, 69, 1138.
12. S. D. Darling and N. Subramanian, J. Org. Chem., 1975, 40, 2851.
13. Z.-F. Xi, W.-X. Zhang, Z.-Y. Song, W.-X. Zheng, F.-Z. Kong and T. Takahashi, J. Org. Chem., 2005, 70, 8785.
14. N. Ajellal, C. M. Thomas and J.-F. Carpentier, Polymer, 2008, 49, 4344.
15. L.-B. Han, Y. Ono and H. Yazawa, Org. Lett., 2005, 7, 2909.
16. (a) L. Wu, B.-L. Li, Y.-Y. Huang, H.-F. Zhou, Y.-M. He and Q.-H. Fan, Org. Lett., 2006, 8, 3605; (b) L. Wu, Z.-W. Li, F. Zhang, Y.-M. He and Q.-H. Fan, Adv. Synth. Catal., 2008, 350, 846; (c) L. Wu, J. Ling and Z.-Q. Wu, Adv. Synth. Catal., 2011, 353, 1452; (d) L. Wu, X. Zhang and Z.-M. Tao, Catal. Sci. Technol., 2012, 2, 707; (e) L. Wu, X. Zhang, Q.-Q. Chen and A.-K. Zhou, Org. Biomol. Chem., 2012, 10, 7859.
17. For rhodium-catalyzed asymmetric hydroarylation of di-phenylphosphinylallenes with arylboronic acids, see: (a) T. Nishimura, S. Hirabayashi, Y. Yasuhara and T. Hayashi, J. Am. Chem. Soc., 2006, 128, 2556; (b) X.-X. Guo, T. Sawano, T. Nishimura and T. Hayashi, Tetrahedron: Asymmetry, 2010, 21, 1730.
18. L.-F. Liu, Y.-H. Zhang and Y.-G. Wang, J. Org. Chem., 2005, 70, 6122.
19. (a) F. K. Sheffy, J. P. Godshalx and J. K. Stille, J. Am. Chem. Soc., 1984, 106, 4833; (b) C. G. Frost, J. Howarth and J. M. J. Williams, Tetrahedron: Asymmetry, 1992, 3, 1089.
20. Another alternative mechanism involving palladium-catalyzed hydroarylation of phosphinoyl-α-allenic alcohols with arylboronic acids ref. 8b described as below is also conceivable. However, it is difficult to rationalize this mechanism since the aliphatic substitutions on allenes would inevitably lead to by-product D via beta-hydride elimination, which are not observed. In addition, the hydrolysis of intermediate B under current conditions towards by-product allylic alcohol (C) should be detected
    .

---

Footnotes

† Electronic supplementary information (ESI) available: Experimental procedures and products characterizations. See DOI: 10.1039/c4ra12251h

‡ Undergraduate participants.

---