Ethyl 4-iodo-2,3,4-trideoxy-α-D-threo-hex-2-enopyranoside: synthesis and dehydroiodination

Abstract

Iodinolysis of ethyl 6-O-benzoyl-4-O-methylsulfonyl-2,3-dideoxy-α-D-erythro-hex-2-enopy-ranoside in the presence of pyridine gives the expected product of inversion, viz. the 4-iodo-2,3,4-trideoxy-α-D-threo congener (8). If, however, the pyridine is omitted, 8 rearranges to give ethyl 6-iodo-4-O-benzoyl-2,3,6-trideoxy-α-D-erythro-hex-2-enopyranoside. Reduction of 8 with lithium aluminum deuteride takes three courses: allylic deuterolysis in the expected SN2′ sense, deuterolysis at C-4 with retention of configuration, and a ring opening reaction giving deuterated hexa-2,4-dien-1,6-diol. Dehydroiodination of 8 with diazabicyclononene gave 1-benzoloxy-6-ethoxy-3(E),5(Z)-hexadiene-2-one in 86% yield.