Synthesis of allylboronic acids and allylboronates
Aliphatic, aromatic, heteroaromatic, vinyl, or allylic Grignard reagents react with pinacolborane at ambient temperature in tetrahydrofuran to afford the corresponding pinacolboronates. The initially formed dialkoxy alkylborohydride intermediate quickly eliminates hydridomagnesium bromide and affords the product boronic ester in very good yield. This reaction also can be carried out under Barbier conditions.
J. W. Clary, T. J. Rettenmaier, R. Snelling, W. Bryks, J. Banwell, W. T. Wipke, B. Singaram, J. Org. Chem., 2011, 76, 9602-9610.
Readily available allylic acetates are converted to allylic boronates catalyzed by Ni/PCy3 or Ni/PPh3 complexes with high levels of stereoselectivity and in good yields, whereas the borylation of allylic halides can be accomplished with commercially available Pd catalysts [e.g., Pd2(dba)3, PdCl2, Pd/C].
P. Zhang, I. A. Roundtree, J. P. Morken, Org. Lett., 2012, 14, 1363-1365.
The use of low-cost iron(III) acetoacetate and tetramethylethylenediamine (TMEDA) enables a mild direct cross-coupling of alkyl halides with bis(pinacolato)diboron at room temperature. Moreover, the borylation of benzylic or allylic chlorides, tosylates, and mesylates is possible. The reactions show broad functional-group compatibility.
T. C. Atack, R. M. Lecker, S. P. Cook, J. Am. Chem. Soc., 2014, 136, 9521-9523.
A copper-catalyzed γ-selective and stereospecific substitution reaction of allylic carbonates with bis(pinacolato)diboron afforded allylboron compounds. Functionalized allylboronates that have an acetal, ester, or isolated alkene were prepared. The reaction of optically active allylic carbonates underwent complete chirality transfer.
H. Ito, C. Kawakami, M. Sawamura, J. Am. Chem. Soc., 2005, 127, 16034-16035.
Cu(I)-catalyzed enantioselective substitution of readily available allylic carbonates with bis(pinacolato)diboron afforded various α-chiral allylboronates, including functionalized allylboronates, with high enantiomeric purity.
H. Ito, S. Ito, Y. Sasaki, K. Matsuura, M. Sawamura, J. Am. Chem. Soc., 2007, 129, 14856-14857.
A remarkably simple and effective system allows a direct conversion of allylic alcohols into high value allylic boronic esters using commercially available reagents and catalysts.
G. Dutheuil, N. Selander, K. J. Szabó, V. K. Aggarwal, Synthesis, 2008, 2293-2297.
A copper-catalyzed synthesis of benzyl-, allyl-, and allenyl-boronates from benzylic, allylic, and propargylic alcohols, respectively, exhibits a broad reaction scope and high efficiency under mild conditions. Preliminarily mechanistic studies suggest that nucleophilic substitution is involved in this reaction.
L. Mao, K. J. Szabó, T. B. Marder, Org. Lett., 2017, 19, 1204-1207.
A copper(I)-catalyzed γ-boryl substitution of allyl acylals enables an enantioselective synthesis of α-chiral γ-acetoxyallylboronates with high E/Z selectivity and enantioselectivity. A subsequent reaction with aldehydes provides monoprotected anti-1,2-diol derivatives with high stereoselectivity.
Y. Takenouchi, R. Kojima, R. Momma, H. Ito, Synlett, 2017, 28, 270-274.
A new method for the synthesis of substituted 2-acylallylmetal reagents in a highly regio- and stereoselective fashion involving a three-component assembly of allenes, acyl chlorides, and bimetallic reagents (B-B, Si-Si, and Sn-Sn) catalyzed by phosphine-free palladium complexes is described.
F.-Y. Yang, M. Shanmugasundaram, S.-Y. Chuang, P.-J. Ku, M.-Y. Wu, C.-H. Cheng, J. Am. Chem. Soc., 2003, 125, 12576-12583.
Palladium-catalyzed coupling reactions of functionalized allylboronic acids with various iodobenzenes under standard Suzuki-Miyaura coupling conditions afforded selectively the branched allylic products in high to excellent yields.
S. Sebelius, V. J. Olsson, O. A. Wallner, K J. Szabó, J. Am. Chem. Soc., 2006, 128, 8150-8151.
In situ generation of allylic boronates by iridium-catalyzed borylation of cyclic alkenes in the presence of additives, such as methylimidazole and DBU, followed a reaction with aldehydes allows the synthesis of stereodefined homoallylic alcohols. Cycloalkenes without additives as well as acyclic substrates gave vinylic boronates, which were coupled with organohalides in a Suzuki-Miyaura sequence.
V. J. Olsson, K. J. Szabó, J. Org. Chem., 2009, 74, 7715-7723.
A chemo-, regio-, and stereoselective iron-catalyzed 1,4-hydroboration of dienes affords γ-disubstituted allylboronates. 1,4-Hydroboration of 2-substituted dienes forms products with (E)-trisubstituted double bonds exclusively.
J. Y. Wu, B. Moreau, T. Ritter, J. Am. Chem. Soc., 2009, 131, 12915-12917.
In the presence of a chiral phosphoramidite ligand, the palladium-catalyzed diboration of allenes can be executed with high enantioselectivity with a range of aromatic and aliphatic allenes. A mechanism is proposed based on isotopic-labeling experiments, stereodifferentiating reactions, kinetic analysis, and computational experiments.
H. E. Burks, S. Liu, J. P. Morken, J. Am. Chem. Soc., 2007, 129, 8766-8773.
Pd-catalyzed diboration of prochiral allenes occurs exclusively at the internal position and is accelerated in the presence of Lewis basic ligands. A chiral ligand was employed, and the enantiomeric excess of a variety of diboration products was found to be in the range of 86-92% ee.
N. F. Pelz, A. R. Woodward, H. E. Burks, J. D. Sieber, J. P. Morken, J. Am. Chem. Soc., 2004, 126, 16328-16329.