Experiments on the synthesis of tetracyclines. Part XII. Extension of the acetal photocyclisation process

Abstract

In analogy to earlier work, the acid-catalysed photocyclisation of 3-[2-(dioxolan-2-yl)benzyl]chromone (II; XX = O·CH₂·CH₂·O) to give 6,6-ethylenedioxy-5aα6,11,11aα-tetrahydro-12H-benzo[b]xanthen-12-one (III) and its trans-(5aαH,11aβH)isomer (IV) has been effected. It is suggested that this photocyclisation process will be of general synthetic utility.