Mitsunobu reaction allene synthesis

Jin and Weinreb reported the enantioselective total synthesis of 5,11-methano-morphanthridine Amaryllidaceae alkaloids via ethynylation of a chiral aldehyde followed by allenylsilane cyclization (Scheme 4.6) [10]. Addition of ethynylmagnesium bromide to 27 produced a 2 1 mixture of (S)- and (R)-propargyl alcohols 28. Both of these isomers were separately converted into the desired same acetate 28 by acetylation or Mitsunobu inversion reaction. After the reaction of 28 with a silyl cuprate, the resulting allene 29 was then converted into (-)-coccinine 31 via an allenylsilane cyclization. 

Reductive Transposition of Allylic Alcohols. In direct anal ogy to the synthesis of allenes from propargylie alcohols, invertlve (Mitsunobu) displacement of aUylic alcohols with NBSH fol lowed by warming of the reaction mixture to ambient temperature to Induce diazene formation and sigmatropic loss of dinitrogen provides reductively transposed alkenes. This methodology has proven to be highly effective for the reductive 1,3 transposition of a wide variety of allylic alcohols (eq 3). ... 

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