85021-22-3Relevant articles and documents
Vilsmeier formylation of tert-anilines: Dibenzo[b,f][1,5]diazocines and quinazolinium salts via the 't-amino effect'
Cheng, Ying,Meth-Cohn, Otto,Taylor, David
, p. 1257 - 1262 (2007/10/03)
The attempted Vilsmeier ortho-formylation of p-substituted N,N-dimethylanilines 1 with N-formyl-N-alkylarylamides 2 unexpectedly gives dibenzo[b,f][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 =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 W-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=NR2+, the 't-amino effect'.
