4- and 5-Oxocarboxylic Acids as Versatile Synthons for the Preparation of Heterocycles

Conversions of 4-and 5-oxocarboxylic acids for the preparation of heterocycles are discussed.The review illustrates the importance and variability and presents the synthetic applicability of these versatile synthons.CONTENTS 1. Introduction 2. Reactions with hydrazines 3. Reactions with hydroxylamine 4. Cyclocondensations with bifunctional amino derivatives 5. Cyclizations to lactones 6. Formation of lactams 7. Conversion to thiophene derivatives 8. Syntheses of natural products.Other ring systems RCOCl AlCl 3 NH 2 NH 2 O O COOH R O 10 O O NH N O R 11 H O O COO 9 Scheme 4In aqueous solution, the sulfuric acid-catalysed reaction of 3-methyl-4-oxopentanoic acid ( 12) with phenylhydrazine gives the indole derivative (13). 60(Scheme 5) R 1 R 2 yield (%) ref. 3-pyridil H 57 49 Ph Ph 43 46 2-thienyl H 40 48 R yield (%) ref.C 6 H 4 Me-4 89 58 C 6 H 4 Cl-4 85 59 + NHNH 2 H 2 O H 2 SO 4 N Me Me COOH 13 O COOH Me Me 12 Scheme 5 The phenylhydrazones of 14 have been cyclized to fused tetracyclic compounds containing an indole moiety (15). 61When R = COOEt, the carbazole (16) was formed.(Scheme 6) n = 2 ( ) n