C-H insertion approach to the total synthesis of furofuran lignans and their heterocyclic analogues

Abstract

The synthesis of novel a-diazo-y-butyrolactones was achieved via diazo-transfer reactions on activated lactones. These were subsequently found to undergo highly efficient regio- and stereo-selective C-H insertions to afford the endo,exo-fuxof\xrmvone motif. This methodology was applied in the synthesis of various bicyclic furofuranone derivatives including two unsymmetrically substituted furofuran lignans, (±)-fargesin and (±)- epimagnolin A. Further investigations into the enantioselective synthesis of furofuran(ones) highlighted l-acetyl-4-aryl-3-oxabicyclo[3.L0]hexanes as key intermediates. Optimisation of alcohol additions to these cyclopropanes under Lewis acidic conditions, with the development of a highly effective diazo-transfer protocol, was successful in the concise and diastereoselective preparation of en<io,gxo-furofuranones. Novel asymmetric synthesis of four endo,exo-fm:ofm2in lignans was also achieved when an enantiomerically enriched 1- aryl-allyl alcohol was employed. A significant contribution to the success of these asymmetric syntheses was the introduction of methanesulfonyl-protected phenols to increase the acid stability of several key intermediates. Furthermore, the convergent nature of this cyclopropane ring-opening approach permitted the formation of diverse structural furofuranone analogues.

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