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DOI: 10.1039/A708799C (Paper) Reference Section for: J. Chem. Soc., Perkin Trans. 1, 1998, 1257-1262

Vilsmeier formylation of tert-anilines: dibenzo[b,f[hair space][hair space]][1,5]diazocines and quinazolinium salts via the ‘t-amino effect’1

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Ying Cheng, Otto Meth-Cohn and David Taylor

Abstract

The attempted Vilsmeier ortho-formylation of p-substituted N,N-dimethylanilines 1 with N-formyl-N-alkylarylamides 2 unexpectedly gives dibenzo[b,f[hair space][hair space]][1,5]diazocines 5 in 26–74% yield. This reaction proceeds by Vilsmeier formylation ortho to the dimethylamino group of 1 followed by hydride migration from the N-methyl group to the newly formed iminium [double bond, length half m-dash]CH group, followed by intramolecular cyclisation, a new example of the ‘t-amino effect’. Similar formylation of cyclic tert-anilines such as 4-tolyl-pyrrolidines 6a,e,g, -piperidines 6b,f,h, -perhydroazepines 6c,i and -morpholine 6d, however, shows a different chemistry giving diformylated enamines 7 as the major products (12–60%). A small amount of diazocines 8 (1–13%) with a substituted benzyl at the nitrogen and N-formylated diazocines 9 are also isolated in some cases. When N-formyl-1,2,3,4-tetrahydroquinoline is used as the Vilsmeier reagent, normal formylation is observed, while use of aliphatic Vilsmeier reagents such as DMF and N-formylmorpholine give quinazolinium salts 16 and 17, also by way of the ‘t-amino effect’. The key feature in these formylations is the hydride transfer from the α-position of a tertiary amine to an unsaturated ortho-substituent CH[double bond, length half m-dash]NR2+, the ‘t-amino effect’.

References

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  11. To be published elsewhere; thanks to Drs D. Eggleston and C. Haltewanger of SB for the X-ray crystallography.
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