Studies in aryne chemistry

The principal methods for the generation of arynes, and the Diels–Alder reactions of steroidal dienes are briefly reviewed. Tetrafluorobenzyne (generated from pentafluorophenyl-lithium and pentafluorophenyl magnesium chloride) reacts with simple models for steroidal diene systems to give mainly 1,4-addition products. Benzyne (generated from o-bromofluorobenzene and anthranilic acid), tetrachlorobenzyne (from tetrachloroanthranilic acid) and tetrafluorobenzyne react with steroidal-5,7-dienes to give products of the ene-reaction. In addition, tetrafluorobenzyne forms a 5,8-adduct with a 5,7-diene and with a 5,7,9(11)-triene. Cholesta-2,4-diene gives 1,4-adducts with benzyne and tetrafluorobenzyne which undergo retro-Diels–Alder reactions on pyrolysis. Steroidal-1(10),9(11)-dienes also give 1,11-adducts with benzyne and tetrachlorobenzyne. The adducts of tetrafluorobenzyne with models for the oestrogen steroids, and with oestradiol dimethyl ether are reported. An unsuccessful attempt to synthesise an adduct from a steroidal styrene is described. Finally the photoisomerisation of 5,6,7,8-tetrafluoro-1,4-dihydro-1,4-ethanonaphthalene is reported and a mechanism proposed.