Highly efficient photometathesis in a proximate, synperiplanar diazene-diazene oxide substrate: retention of optical purity, mechanistic implications

Abstract

In a specifically designed proximate and almost perfectly synperiplanar diazene–diazene oxide substrate, metathesis is the exclusive photoreaction and occurs with retention of optical purity, providing support for the [π2 + π2]photocycloaddition pathway (tetrazetidine oxide intermediate).

References

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6. All compounds have been fully characterized (¹H, ¹³C NMR, MS, UV, IR). Selected data for 4: δ_H(CDCl₃, 400 MHz) 5.47 (dd, J_7,8=J_8,9 1.6, 8-H), 5.31 (dd, J_1,2=J_1,13 1.6, 1-H), 2.35 (ABXY, J_AB 10.4, 7-H), 2.27 (ABXY, J_AB= 10.4, 2-H), 2.32–2.25 (dddd, 9-H), 2.23–2.15 (dddd, 13-H), 1.80–1.70 (m, 10a-H, 12a-H), 1.47 (s, 6-Me), 1.45–1.35 (m, 10s-H, 11a-H, 12s-H), 1.39 (s, 3-Me), 1.23–1.10 (m, 11s-H), 0.92 (s, 16s-Me), 0.72 (s, 16a-Me); δ_C(CDCl₃, 100.6 MHz) 91.0 (C-3), 75.6 (C-6), 64.0 (C-8), 63.6 (C-1), 59.8 (C-16), 48.3 (C-7), 44.6 (C-13), 43.7 (C-9), 43.3 (C-2), 30.2/29.9 (C-10, C-12), 26.2 (C-11), 17.4 (16-Me anti), 15.6 (16-Me syn), 12.1 (6-Me), 9.7 (3-Me); m/z(EI) 201 [M⁺– Me – N₂– N₂O](5%), 141 [tetramethyl-4H-pyrazole N-oxide + H⁺](100), 125 [tetramethyl-4H-pyrazole + H⁺](26), 91 (39); λ_max(CH₃CN)/ nm 204 (ε/dm³ mol^–1 cm^–1 4620), 237 (3780), 387 (81). ν(KBr)/cm^–1 1509 (NNO). Selected data for 5: δ_H(CDCl₃, 400 MHz) 4.38 (dd, J_9,10 9.2, J_10,14 7.0, 10-H), 4.10 (dd, J_4,5 5.9, J_4,15 6.4, 4-H), 2.79–2.69 (dddd, 9-H), 2.58 (dd, J_4,15= 6.4, J_14,15 10.4, 15-H), 2.45–2.35 (m, i. a. 5-H), 2.25–2.19 (m, 8-H), 2.15 (dd, J_10,14= 7.0, J_14,15 10.4, 14-H), 2.11–1.96 (m, 2 H), 1.93–1.85 (m, 1 H), 1.84 (s, Me), 1.59–1.48 (m, 7-H), 1.40 (s, Me), 1.05 (s, Me), 1.02 (s, Me): δ_C(CDCl₃, 100.6 MHz) 105.4 (C-13), 98.5 (C-1), 86.5 (C-10), 65.7 (C-4), 49.3 (C-16), 45.4 (C-15), 41.0 (C-14), 37.2 (C-9), 36.7 (C-5), 31.5/30.1 (C-6, C-8), 26.1 (C-7), 25.2/17.2/16.9/15.0 (CH₃); m/z(EI) 288 [M⁺](2%), 244 [M⁺–N₂O](1), 216 [M⁺– N₂– N₂O](28), 201 [M⁺– N₂– N₂ O – Me](100), 133 (60); λ_max(CH₃CN)/nm 239 (ε/dm³ mol^–1 cm^–1 5510), 346 (172); ν_max(KBr)/cm^–1 1509 (NNO).
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