Enantioselective synthesis of 2-methyl-1,2-syn- and 2-methyl-1,2-anti-3-butenediols via allene hydroboration-aldehyde allylboration reaction sequences

Academic Article
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publication date

  • October 2009

abstract

  • The hydroboration of allene 7 with ((d)Ipc)(2)BH at 0 degrees C provides the kinetic allylborane 12Z with >20:1 selectivity. However, when the hydroboration is performed at 85 degrees C, the kinetically formed allylborane isomerizes to give the thermodynamic allylborane 12E with >or=12:1 selectivity. Subsequent treatment of 12Z or 12E with aldehydes at -78 degrees C, followed by oxidative workup, provides the 2-methyl-1,2-diols 8 and 9 in good yield and with 80-92% e.e.