STEREOSELECTIVE PREPARATION OF 6β-SUBSTITUTED PENICILLANATES. TRI-ORGANOTIN HYDRIDE REDUCTION OF 6-ISOCYANO-, 6-PHENYLSELENENYL-, 6-HALO-, AND 6-ISOTHIOCYANATO-PENICILLANATES

Article abstract of DOI:10.1016/S0040-4020(01)92141-6

6β-Benzyl-, 6β-(2-hydroxyprop-2-yl)-, 6β-methoxycarbonylmethyl-, 6β-methoxycarbonylethyl-, 6β-(t-butoxycarbonylmethyl)-, and 6β-methylthiopenicillanates 10-15 have been prepared stereoselectively by tri-n-butyltin hydride reduction of the corresponding 6β-isocyanopenicillanates 4-9.A minor side-product (15percent) isolated from the reduction of benzyl 6α-(2-hydroxyprop-2-yl)-6β-isocyanopenicillanate 5 was identified as (1R,5R)-6-<(1R)-1-benzyloxycarbonyl-2-methylprop-1-yl>-1-(2-hydroxyprop-2-yl)-2,6-diaza-4-thiabicyclo<3,2,0>hept-2-en-7-one 18, and small quantities of analogous thiazolines 19 and 20 were detected in the crude mixtures from the reductions of the 6α-benzyl- and 6α-methoxycarbonylmethyl-6β-isocyanopenicillanates 4 and 6.Benzyl and methyl penicillanates 30 and 31 were obtained by tri-n-butyltin hydride reduction of the 6α-brompenicillanates 28 and 29, and reduction of benzyl 6,6-dibromopenicillanate 35 gave a mixture of products in wich the 6β-bromopenicillanate 37 predominated. 6β-Chloro-, 6β-phenylselenenyl-, and 6β-allylpenicillanates 48, 49 and 52 were obtained by tri-n-butyltin hydride reduction of the corresponding 6-phenyl- selenenylpenicillanates 43, 45, 50 and 51. In contrast, tri-organotin hydride reduction of methyl 6β-isothiocyanatopenicillanate 53 was accompanied by sulphur-C(2) bond cleavage to give rearranged thiazoline-azetidinones 54 and 55.