Stereoselective Domino Semipinacol‐Schmidt Reaction: Diastereoselective Synthesis of 7 a‐epi‐(+)‐Lepadiformine C and Formal Synthesis of 7 a‐epi‐(−)‐Lepadiformine A

A concise approach has been developed for the diastereoselective synthesis of the azatricyclic core of (−)‐7 a‐epi‐lepadiformine A (8 a) and (−)‐7 a‐epi‐lepadiformine C (8 b) using stereoselective domino semipinacol‐Schmidt reaction as a key step. In presence of TiCl4, the oxaspiropentane‐azide derivatives underwent stereoselective domino cyclization to furnish the corresponding angularly fused azatricyclic cores in very good yields. Moreover, azatricyclic core of (−)‐7 a‐epi‐lepadiformine A has also been realized, in a stepwise manner, through the intramolecular Schmidt reaction of azido‐spirocyclobutanone intermediate. The synthetic utility of domino semipinacol‐Schmidt reaction is further shown in the diastereoselective synthesis of (+)‐7 a‐epi‐lepadiformine C (7). A TiCl4 Lewis acid‐mediated domino semi‐pinacol‐Schmidt reaction‐based approach has been developed for the diastereoselective synthesis of 7 a epi‐lepadiformine C (+)‐7 and azatricyclic core of 7 a epi‐lepadiformine A (+)‐8 a.