Experiments of the synthesis of tetracycline. Part V. Photocyclisation of ring B

Abstract

The ethylene acetal of 4-(2-formylbenzyl)-2phenylnaphtho[1,8-bc]furan-5-one (III; XY = O) has been cyclised under acid-catalysed photolytic conditions to 12-ethylenedioxy-6α,7,12,12aα-tetrahydro-1-phenylnaphthaceno[1,12-bc]furan-6-one (V; XY = O·CH₂·CH₂·O). This method of establishing the linear tetracyclic carbon skeleton has been extended to dithio and monothio-acetals, and to the parent aldehyde (III; XY = O) itself.