Stereoselectivity of N-benzyl-C-ethoxycarbonyl nitrone cycloaddition to (S)-5-hydroxymethyl-2(5H)-furanone and its derivatives

Stereoselectivity of the reaction of N-benzyl-C-ethoxycarbonyl nitrone (3) with (S)-5-hydroxymethyl-2(5H)-furanone (2a) and its 5-alkoxy substituted d erivatives 2b-f was investigated. The reaction proceeds in a highly face-se lective manner, the products 4-6 resulting from approach anti to the hydrox ymethyl or alkoxymethyl group of the dipolarophile. The exo-stereoselectivi ty increases as the size of protective group attached to lactone (2b-f) inc reases. Endo-exo diastereoselectivity is affected significantly by the solv ent. Microwave irradiation strongly accelerates the reaction with little ef fect on the diastereoselectivity to give the syn adduct 8a in addition to a nti cycloadducts 4a-6a. (C) 1999 Elsevier Science Ltd. All rights reserved.