Synthesis of New Enantiopure Bicyclic 1,2‐Oxazines by Addition of Lithiated Methoxyallene to Chiral Cyclic Nitrones

A highly diastereoselective addition of lithiated methoxyallene 3 to chiral cyclic nitrones 1 and 2 provided N ‐hydroxy pyrrolidines 4 and 5 , respectively, which cyclized to bicyclic 1,2‐oxazines 6 and 7 by simple stirring in dilute CH 2 Cl 2 solution. Storage of 4 in a more concentrated solution led to formation of a 60:40 mixture of 1,2‐oxazine 6 and amine oxide 8 . Hydroboration of 7 furnished the hydroxy‐substituted bicyclic 1,2‐oxazine 9 with excellent diastereoselectivity. Hydrogenolysis of 6 provided the substituted pyrrolidine derivative 10 . (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)