Enantioselective synthesis of 2-methyl-1,2-syn- and 2-methyl-1,2-anti-3-butenediols via allene hydroboration-aldehyde allylboration reaction sequences.
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.
Chen
Ming
M
Department of Chemistry, Scripps Florida, Jupiter, Florida 33458, USA.
Handa
Masaki
M
Roush
William R
WR
D000438:Alcohols / Q000138:chemical synthesis* / Q000737:chemistry*; D000447:Aldehydes / Q000737:chemistry*; D000466:Alkadienes / Q000737:chemistry*; D001895:Boron / Q000737:chemistry*; D013237:Stereoisomerism; D013379:Substrate Specificity
D000438:Alcohols; D000447:Aldehydes; D000466:Alkadienes; C025947:propadiene; D001895:Boron