An efficient synthesis of 3-aza-steroids bearing a pyridine as an A ring was achieved via intramolecular cycloaddition of orthoquinodimethanes, which were generated from a 3-azabicyclo[4.2.0]octa-l,3,5-trien-7-one ketal.
A new strategy for introducing an hydroxy group at the position 3 of an aromatic A ring in a steroid, which is a key position for biological purposes, is described. This procedure has required a judicious choice of a t-butyl ether as protectivegroup at the beginning of the synthesis, and its deprotection can be achieved in high yield in the final step.
The alkylation of the (+/-)-spiro-gamma-lactones 1 and 5a occurs with high diastereofacial selectivity. Geometry-optimized ab initio 4-31G calculations on enol 7 suggest that electrophilic attack occurs at an angle of about 80 degrees to the plane of the enolate, together with a displacement of the trajectory away from the oxygen linked to lithium.
A five step synthesis of (d,l)-estrane derivatives from 1,3-butadiene
We set out to describe a new and versatile method for preparing 3-aza-11-oxa-1,3,5(10)-trieno steroids via an intramolecular Diels-Alder cycloaddition of o-quinodimethanes as the key step. The characteristic H-1 and C-13 NMR spectroscopic features of the synthesized compounds are reported. (c) 2006 Elsevier Inc. All rights reserved.