A STRAIGHTFORWARD SYNTHETIC APPROACH TO THE SPIROKETAL-ENOL ETHERS SYNTHESIS OF NATURAL ANTIFEEDING COMPOUND TONGHAOSU AND ITS ANALOGS

Tonghaosu 1, a natural product discovered from several plants of tribe Athemdeae, is a [4.4]spiroketal with an enediyne side-chain and shows interesting insect antifeeding activity. In this paper a general and convenient synthetic methodology for the synthesis of 1, 2 and its spi roketal-enol ether derivatives is described. Thus, 3-(2'-furyl)-propan -1-ol 7a or 4-(2'-furyl)-butan-1-ol 7b prepared from furaldehyde was t reated with n-butyl lithium and unsaturated aldehyde to provide the di ol 5. Diol 5 could also be obtained from 5-(3-acetoxypropyl)-2-furalde hyde or 5-(4-acetoxybutyl)-2-furaldehyde and alkynyllithium. By carefu l treatment of 5 or 7 with acid, dehydration-cyclization occurred to g ive the desired spiroketal-enol ether in moderate to excellent yields. (C) 1998 Elsevier Science Ltd. All rights reserved.