A
new method for the chemoselective reduction of aldehydes and ketones
using
boron tri-isopropoxide, B(OiPr)3:
Comparison with boron
tri-ethoxide,
B(OEt)3
BURCU UYSAL and
BIRSEN S OKSAL*
Department of
Chemistry, Akdeniz University, 07058, Antalya, Turkey
e-mail:
bbirsen@akdeniz.edu.tr
MS received 24
September 2010; revised 13 April 2011; accepted 6 June 2011
Abstract.
A chemoselective Meerwein–Ponndorf–Verley reduction process of
various aliphatic and allylic
α,β-unsaturated
aldehydes and ketones is described. This chemoselective reduction is catalysed
by boron triisopropoxide
B(Oi Pr)3.
Kinetics of reduction of aldehydes and ketones to corresponding alcohols were
also
examined and rate
constant of each carbonyl compounds were measured. Rate constant and reduction
yield of
each carbonyl
compounds in the presence of B(Oi Pr)3 were
compared with those in the presence of B(OEt)3.
The alcohols that
are the reduction product were analysed by GC-MS. The rate constants and
alcohol yields
were found to be
higher with B(OEt)3 than with B(Oi Pr)3.
The mechanism proposed involves a six-membered
transition state in
which both the alcohol and the carbonyl are coordinated to the same boron
centre of a boron
alkoxide catalyst.
Graphical
Abstract. A
chemoselective Meerwein–Ponndorf–Verley (MPV) reduction of various
aliphatic and allylic α,β-unsaturated
aldehydes and ketones in the presence of
boron tri-isopropoxide B(OiPr)3 is
described. The results are compared with
those obtained in the presence of
B(OEt)3.
Keywords.
Boron tri-iso-propoxide; boron tri-ethoxide; chemoselective
reduction; allylic alcohols;
Meerwein–Ponndorf–Verley reduction.