Modified Danheiser

This reaction has been successfully applied to cyclopentenone annelation onto cycloalkenes. By modifying Danheiser s protocol [15], alkynyl-substituted bi-cyclo[n.l.0]alkanol derivatives are prepared by the reaction of gem-lithio-bromocyclopropanes 27 with alkynylborons, as shown in Scheme 10. 

R.L. Danheiser and co-workers have used the modified Danheiser benzannuiation for the synthesis of the marine carbazole alkaloid hyellazole. The required diazoketone was prepared from the A/-Boc derivative of 3-acetylindole using a diazo transfer reaction. The diazoketone was irradiated in the presence of the alkyne to afford the desired carbazole annulation product in 56% yield. Finally, in order to install the phenyl group of hyellazole at Cl, the phenolic hydroxyl group was converted to the corresponding triflate and a Stiiie cross-coupiing was performed. 

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