Simple and condensed β-lactams.: Part 33.: AlCl3 catalyzed ring closures of some 3-aryloxy-4-oxoazetidine-2-carboxylic chlorides to 1H-chromeno[3,2-b]azete-2,8(2aH,8aH)-diones and some reactions of the products

lCarboxylic chlorides 3a-3c, when treated with AlCl3, afforded the tricyclic compounds 17a-17c. NaBH4 reduction of 17a and 17b afforded compounds 11a and 11b. The latter and the related known compounds 4a, 5b, 6a and 7a were used for the preparation of various dihydrochromeno[3,2-b]azet-2(1H)-ones and of a 3,4-disubstituted chromane-2-carboxylic ester (26) of fixed stereochemistry. Catalytic reduction of 8-chloro compound 5b afforded compounds 10b and 25, the products of simple hydrodechlorination and of azetidinone ring cleavage with concomitant hydrodechlorination, respectively. (C) 1999 Elsevier Science Ltd. All rights reserved.