(Z)-3-Alkylidene-4,5-dihydro-4-hydroxy-5-methyl-2-(3H)-furanones by Regio- and Diastereo-selective Ene Reaction of Singlet Oxygen (Schenk Reaktion) with γ-Hydroxy Vinylstannanes: An Enantioselective Synthesis of Dihydromahubanolide B

Waldemar Adam; Peter Klug

doi:10.1055/s-1994-25525

Synthesis 1994; 1994(6): 567-572
DOI: 10.1055/s-1994-25525

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(Z)-3-Alkylidene-4,5-dihydro-4-hydroxy-5-methyl-2-(3H)-furanones by Regio- and Diastereo-selective Ene Reaction of Singlet Oxygen (Schenk Reaktion) with γ-Hydroxy Vinylstannanes: An Enantioselective Synthesis of Dihydromahubanolide B

Waldemar Adam^* , Peter Klug

^*Institute of Organic Chemistry, University of Würzburg, Am Hubland, D-97074 Würzburg, Germany

Abstract

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(Z)-3-Alkylidene-4,5-dihydro-4-hydroxy-5-methyl-2-(3H)-furanones 5 were prepared from appropriately substituted propargylic alcohols 1 by a sequence of hydromagnesation to γ-hydroxy vinylstannanes 2, subsequent photooxygenation and reduction to stannyl diols 3, iododestannylation to iodo diols 4, and finally cyclization by palladium-catalyzed carbonylation (for 5a) or Ni(CO)₂(PPh₃)₂ (for 5b,c). The reaction sequence can be performed enantioselectively by starting with chiral propargylic alcohols. The current approach constitutes a convenient four-step synthesis of optically active lactones 5 from readily available starting materials and is applied herein to the preparation of the natural lactone dihydromahubanolide B.

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