[2+2]Cycloaddition of chlorosulfonyl isocyanate to (Z) 3-O-(2'- silylvinyl) ethers of 1,2-O-isopropylidene-5-O-trityl-α-D-xylofuranose

Article abstract of DOI:10.1016/S0040-4020(98)00857-6

The asymmetric [2+2]cycloaddition of chlorosulfonyl isocyanate to 1,2- O-isopropylidene-3-O-(2'-silylvinyl)-5-O-trityl-α-D-xylofuranoses proceeds with high stereoselectivity in a good yield to afford the corresponding azetidin-2-ones with (R) configuration at the newly formed stereogenic center. The bulky t-butyldimethylsilyl substituent causes partial epimerization at C-3' carbon atom of the azetidin-2-one ring. Intramolecular alkylation of the nitrogen atom by the terminal carbon of the sugar chain gives 1-oxacephams; basic conditions of cyclization cause desilylation or partial desilylation of products.