Hydroboration of alkenes with BH3: A ″hot″ reaction at room temperature in solution

ORGN 516

Yatsandra Oyola, yoyola@mail.chem.tamu.edu, Department of Chemistry, Texas A&M University, College Station, TX 77840 and Daniel A. Singleton, singleton@mail.chem.tamu.edu, Department of Chemistry, Texas A & M University, College Station, TX 77843.
The mechanism of hydroboration of alkenes with BH3 has been explored by a combination of experimental and theoretical studies.  A striking observation is that the regioselectivity of hydroboration of terminal alkenes is lower than can be accounted for by transition state theory.  We propose that the observed regioselectivity is that of a ″hot″ reaction, resulting from the combination of an exothermic association of alkene with borane to form an intermediate complex.  This complex then faces low barriers to anti–Markovnikov and Markovnikov product formation and reacts faster than the excess energy is lost to solvent.  Alternative possible origins for the discrepancy between the theoretically predicted and experimental selectivity are considered, and RRKM and dynamic trajectory analyses of the regioselectivity are discussed.

 

Physical Organic Chemistry, Metal-Mediated Reactions, Asymmetric Reactions and Syntheses
8:00 PM-10:00 PM, Tuesday, August 21, 2007 BCEC -- Exhibit Hall - B2, Poster

Division of Organic Chemistry

The 234th ACS National Meeting, Boston, MA, August 19-23, 2007