Conformational analysis of stereoisomeric dodecahydropyrido[2,1-b]-quinazolin-11-ones

Abstract

The structure and conformations of dodecahydropyrido[2,1-b]quinazolin-11-one diastereoisomers, prepared from the corresponding decahydro-derivatives by hydrogenation, have been established by ¹³C and ¹H n.m.r. spectroscopy. Evidence has been found that the situations of the hydrogen atoms attached to the angular C-4a, C-11a, and C-5a correspond to the α,β,α;α,α,α; and α,α,β configurations. In the cisα,α,α product the conformational equilibrium is shifted towards that conformer in which N-5 is axial with respect to ring A, whereas in the α,α,β product the CO group assumes the axial position. The configuration of the lone pair of N-5 has been determined as well.