SN2′ Regio and Stereoselective Alkylation of Allylic and Propargylic Mesylates Linked to a N-Boc Oxazolidine using Organocuprates

N-Boc-oxazolidines derived from (R)-phenylglycinol and bearing a stereodefined propargylic or allylic alcohol side chain were transformed into the corresponding mesylates. Alkylation of these allylic mesylates by means of organocuprate reagents effected a regio and stereoselective 1,3-transfer of chirality. Similarly, alkylation of the propargylic mesylate gave a chiral allenyl oxazolidine. The N-Boc-2-alkenyl oxazolidines resulting from an anti SN2′ addition underwent an intramolecular bromocarbamoylation with a high level of stereocontrol upon treatment with NBS. After reaction with sodium alkoxide, the resulting cyclic urethanes gave the corresponding epoxy oxazolidines whose reactivity towards organocuprates was studied. The sequence represents an efficient synthesis of enantiopure protected aldehydes bearing three contiguous chiral centers.