Benzocarbapenems from indoles

The 8,8a-dihydroazeto[l,2-a]indol-2(1H)-ones (benzocarbapenems) 1a, 16, 17, 22, 27, 35 and 36 have been prepared by cyclodehydration of the corresponding beta-amino acids, these amino acids being obtained by reduction of the analogous 2-substituted or 2,7-disubstituted indoles. The hydroxy group of compound 36 is designed to mimic the carboxylic acid function of the carbapenems on the basis of molecular modelling. The azetidinones 1a and 27, which are unsubstituted at the methylene group of the four-membered ring, are unstable and highly susceptible to ring opening by nucleophiles but the compounds 22, 35 and 36 with two methyl substituents at this position are much more stable. The carbonyl stretching frequency in the IR is close to 1770 cm(-1) for all the azetidinones except the phenol 36 for which the absorption is at 1735 cm(-1). An X-ray crystal structure of compound 36 is reported.