COMMUNICATION
DOI: 10.1002/chem.201103572
One-Pot Three-Component Highly Selective Synthesis of
Homoallylboronates by Using Metal-Free Catalysis
Ismail Ibrahem,*[a] Palle Breistein,[a] and Armando Cꢀrdova*[a, b, c]
The development of catalytic multicomponent and
alkenes are rare. In pioneering work, Hoveyda and co-work-
À
tandem reactions that involve the formation of C C and C-
ers first disclosed the metal-free catalytic b-boration of a,b-
unsaturated ketones and esters.[10] Later Fernꢀndez reported
another metal-free system for this transformation.[11] How-
ever, the metal-free catalytic conjugate borane addition to
enals has not been reported. In this context, we recently dis-
closed a catalytic one-pot three-component enantioselective
heteroatom bonds in one-pot is an important research field
within organic synthesis.[1] These types of transformations
serve as versatile tools for constructing valuable molecules
as well as reducing multiple isolation steps, generation of
waste, and solvents. In this context, the catalytic Petasis re-
action, which is the multicomponent transformation between
an aldehyde, an amine, and a vinyl or aryl boron reagent, is
a very useful reaction for the
homoallylborane synthesis aided by
a combination of
copper and chiral amine catalysts [reaction (1)].[12]
synthesis of functional amines.[2]
Moreover, organoboron com-
pounds such as homoallyl- and
allylboronates represent valua-
ble synthetic organic intermedi-
ates and has received significant
attention in chemical synthe-
sis.[3] For example, homoallyl-[3k–n] and allylboronates are
useful nucleophiles and important starting materials for the
synthesis of alcohols and amines by addition to aldehydes
and imines, respectively.[3b–c] Thus, the development of effi-
cient catalytic methods for the synthesis of boron-containing
compounds is an important research field in chemical syn-
thesis.[4,5] In this context, the metal-catalyzed conjugate addi-
tion of diborons to electron-deficient olefins is one of the
dominated methods for the synthesis of chiral organoboron
compounds.[3k,5–8] The development of metal-free methodol-
ogies is an important task in organic synthesis.[9] On the
other hand metal-free boron additions to electron-deficient
This one-pot three-component reaction between bis(pina-
colato)diboron (B2ACHTNUTRGNE(NUG pin)2) 1, enals 2, and Wittig compounds
3 is an alternative for a possible selective 1,6-addition of
1 to A to give homoallylboranes 4. However, the direct
copper-catalyzed addition of 1 to 2,4-dienoate esters A gives
exclusively the 1,4-addition products B [reaction (2)].[12]
Based on the importance of development of metal-free
technologies and our research interest in this field, we
wanted to investigate and develop a metal-free version of
the one-pot three-component reaction between bis(pinacol-
[a] Prof. Dr. I. Ibrahem, Dr. P. Breistein, Prof. Dr. A. Cꢁrdova
Department of Natural Sciences
Engineering and Mathematics
Mid Sweden University
SE-851 70 Sundsvall (Sweden)
Fax : (+46)8-154908
ACHUTNGRENUNaG to)diboron (B2ACHTUNGTRENN(UGN pin)2) 1, a,b-unsaturated aldehydes 2, and
2-(triphenylphosphoranylidene)acetate esters 3 (Scheme 1).
However, the catalytic b-boration of enals 2 can either un-
dergo 1,4-addition or 1,2-addition to form 5 or 5’, respective-
ly (Scheme 1). High 1,4-selectivity had to be acquired to
achieve a useful protocol for the one-pot three-component
synthesis of homoallylboranes 4. We envisioned that this
could be possible by using a small organic nucleophile (e.g.,
N-heterocyclic carbene (NHC), PPh3 and amine) for the ac-
[b] Prof. Dr. A. Cꢁrdova
Department of Organic Chemistry
The Arrhenius Laboratory, Stockholm University
106 91 Stockholm (Sweden)
[c] Prof. Dr. A. Cꢁrdova
The Berzelii Center EXSELENT
Stockholm University, 106 91 Stockholm (Sweden)
À
tivation of the B B bond of 1 towards conjugate boron ad-
dition to a,b-unsaturated aldehydes 2 (nucleophilic activa-
Supporting information for this article is available on the WWW
tion).[10,11] In addition, it could be possible to improve the
Chem. Eur. J. 2012, 18, 5175 – 5179
ꢂ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
5175