Studies on the total synthesis of gibberellins. A new strategy for A-ring construction

Abstract

3-(4',6'-Dimethoxynaphthalen-1'-yl)propanoic acid (10) was transformed to 8-methoxy-5-(3'-oxo- butyl)-1,2,3,4-tetrahydronaphthalene-2-carboxyic acid (8) and its 2-hydroxy derivative (9) by conventional synthetic reactions. Acid-catalysed cyclization of the derived diazomethyl ketones (23), (24) and (25) led to dienones (26), (27) and (28) which readily underwent base-catalysed 1,4-conjugate addition to provide the hydroethanophenanthrenetriones (30), (31) and (32) respectively.