Althaus M.

Andersen M. W.

Batey R. A.

Beckmann E.

Blais J.

Brown H. C.

Bubnov Y. N.

Carosi L.

Chemler S. R.

Chen M.

Christine L. Willis

Cmrecki V.

Cole T. E.

Denmark S. E.

Fang G. Y.

Flamme E. M.

Gonzalez A. Z.

Guzman-Martinez A.

Hancock K. G.

Helen K. Scott

Hesse M. J.

Hoffmann R. W.

Ito H.

Jack L.-Y. Chen

Kennedy J. W. J.

Kister J.

Kliman L. T.

Kramer G. W.

Lachance H.

Larouche-Gauthier R.

Matteson D. S.

Matthew J. Hesse

Midland M. M.

Park J. K.

Pelz N. F.

Peng F.

Pietruszka J.

Posseme F.

Pulis A.

Ramachandran P. V.

Shiner C. S.

Sonawane R. P.

Stymiest J. L.

Varinder K. Aggarwal

Webster M. P.

Woodward A. R.

Yamamoto Y.

Zschage O.

English

Crossref

ChemInform

ChemInform Abstract: Highly Diastereo- and Enantioselective Allylboration of Aldehydes Using α-Substituted Allyl/Crotyl Pinacol Boronic Esters via in situ Generated Borinic Esters.

Journal of the American Chemical Society

Highly Diastereo- and Enantioselective Allylboration of Aldehydes using α-Substituted Allyl/Crotyl Pinacol Boronic Esters via in Situ Generated Borinic Esters

Readily available, alpha-substituted allyl/crotyl pinacol boronic esters often give low E/Z selectivity (with Z favored) in reactions with aldehydes. We found that addition of nBuLi to the pinacol boronic ester followed by trapping of the alkoxide with TFAA leads to an intermediate allyl borinic ester which undergoes allylboration with very high E selectivity. The substrate scope includes primary to tertiary alkyl alpha-substituents, crotyl substrates, and the previously unreported beta-methallyl pinacol boronic esters. The latter give very high Z selectivity under standard conditions which is completely reversed to high E selectivity under the new conditions. Monitoring the reaction by B-11 NMR confirmed that the reaction proceeds through a borinic ester intermediate.</p

Chen, Jack L. -Y.

Scott, Helen K.

Hesse, Matthew J.

Willis, Christine L.

Aggarwal, Varinder K.

Explore Bristol Research

122, 1777; c

126, 16328; c

3-borotropic shift followed by allylation:

5011; c

78, 323. Reviews; b

Aldrichimica Acta

analysis of the intermediate formed showed a signal at ~51 ppm. The fact that the use of all three additives result in the formation of intermediates with similar signals

Chemical shift in accordance with borinic esters found in literature: Cole,

Chemical shifts in accordance with those found in the literature: Cole,

comprehensive review of allylation reaction using allylboron reagents by

In certain cases this can be controlled: a

NMR has also been used to analyse the intermediates formed when AcCl or CCl3COCl is used as the additive (in place of TFAA) in the allylation.

Protodeboronation of these substrates also led to high Z selectivity (>95:5). Both allylboration and protodeboronation are believed to occur through similar transition states. For a discussion see:

The generality and scope of these methods is either limited by the method of generation of the borinic acid (ref. 10a) or is non-selective (ref

The α-products (1:1 mixture of diastereomers) originate from

There is a single report by Morken describing allylboration of related β-boryl α-substituted pinacol boronic esters where high Z selectivity was also observed: