Studies on extensions of tert-amino effect: Ring-fusion to bridged biaryls and steroids

Studies on extensions of tert-amino effect: Ring-fusion to bridged biaryls and steroids The term t (later tert)-amino effect was introduced by Meth-Cohn and Suschitzky to generalize the thermal isomerization of ortho-substituted tertiary anilines to benzo-fused heterocyclic systems. In type 2 reactions, an ortho-vinyl tert-aniline gives a tetrahydroquinoline via C-C bond formation between the beta-vinyl carbon and the alfa-methylene carbon of the amino group; the reaction could be extended to heterocyclic and bi- and tri-aryl analogues of anilines to obtain novel medium or larger ring systems. It has recently received much attention due to its wide scope and predictable regio- and stereoselectivity. In the present work we report on our efforts to extend the type 2 tert-amino effect to non-conjugated systems, including: I) biaryls connected with a saturated chain bearing the vinyl and the amino moieties in ortho-ortho position in the aromatic rings; II) steroids possessing vinyl and amino substituents in the D-ring Concerning the biaryl compounds, a methylamino-N-methyl or a CH2-O chains were used. In the first case (methylamino-N-methyl chain), the presence of two amino groups positioned ortho to a vinyl substituent in the same molecule, a priori, could lead to three different hydrogen migrations and, accordingly, different types of cyclizations. Although, isomerizations with the involvement of N-methyl group with a preference over the involvement of an N-benzyl might not be expected to take place at all, possible formations of six- and/or ten-membered rings (with N-benzyl carbons) could be considered. Not surprisingly, our isomerization experiment led to a six-membered ring. In case of the CH2-O chain, although, according to DSC, a possible ring closure reaction might have taken place in temperature range of 158-191.11 °C, the corresponding cyclized product, could not be found in our preparative experiments Next, as a fully unexplored field of tert-amino effect, steroids were investigated. We prepared steroids properly functionalized in D-ring to study type 2 tert-amino effect in a non-aromatic system and utilize the isomerization reaction to open a new way to D-fused steroid-ring systems. Cyclization of these steroids did indeed occurred at high temperature to give two diastereomers in a ca. 1:1 ratio.