[2-O-(2-SILYLVINYL) ETHERS OF NE-5-O-TRITYL-ALPHA-D-XYLOFURANOSE(2]CYCLOADDITION OF CHLOROSULFONYL ISOCYANATE TO (Z) 3)

The asymmetric [2+2]cycloaddition of chlorosulfonyl isocyanate to 3-O- 2'-silylvinyl)-5-O-trityl-alpha-D-xylofuranose proceeds with high ster oselectivity in a good yield to afford the corresponding azetidin-2-on es with (R) configuration at the newly formed stereogenic center. The bulky t-butyl-dimethyisilyl substituent causes partial epimerization a t C-3' carbon atom of the azetidin-2-one ring. Intramolecular alkylati on of the nitrogen atom by the terminal carbon of the sugar chain give s 1-oxacephams; basic conditions of cyclization cause desilylation or partial desilylation of products. (C) 1998 Elsevier Science Ltd. All r ights reserved.