S(N)2 ' 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 stereodefi ned propargylic or allylic alcohol side chain were transformed into the cor responding mesylates. Alkylation of these allylic mesylates by means of org anocuprate reagents effected a regio and stereoselective 1,3-transfer of ch irality. Similarly, alkylation of the propargylic mesylate gave a chiral al lenyl oxazolidine. The N-Boc-2-alkenyl oxazolidines resulting from an anti S(N)2' 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 oxaz olidines whose reactivity towards organocuprates was studied. The sequence represents an efficient synthesis of enantiopure protected aldehydes bearin g three contiguous chiral centers. (C) 2000 Elsevier Science Ltd. All right s reserved.