A straightforward synthetic approach to the spiroketal-enol ethers synthesis of natural antifeeding compound tonghaosu and its analogs

Article abstract of DOI:10.1016/S0040-4020(98)00732-7

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 spiroketal-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 treated with n-butyl lithium and unsaturated aldehyde to provide the diol 5. Diol 5 could also be obtained from 5-(3-acetoxypropyl)-2-furaldehyde or 5-(4- acetoxybutyl)-2-furaldehyde and alkynyllithium. By careful treatment of 5 or 7 with acid, dehydration-cyclization occurred to give the desired spiroketal- enol ether in moderate to excellent yields.