Expanding the scope of transformations of organoboron species: carbon–carbon bond formation with retention of configuration

Abstract

The use of boron chemistry for the synthesis of enantiomerically enriched organic compounds is described. Key advances towards the preparation of organoboranes with control of stereochemistry are supplemented by a discussion of the use of these chiral organoboranes in carbon-carbon bond forming reactions. Particular emphasis is given to advances in the Suzuki-Miyaura coupling of chiral secondary organoboranes and homologation reactions. Both of these reactions convert the initially generated B-C bond into a C-C bond and thus lead to a significant increase in complexity.

Borohydrides from Organic Hydrides: Reactions of Hantzsch’s Esters with B(C6F5)3

“…The N-substituted substrates (N-Me, N-Ph) reacted in high yield 90-98 % and the connectivity of the products were confirmed by an X-ray crystallographic analysis of the N-Me borohydride salt 2 a. Unsubstituted Hanztschs ester 1 a reacted less effectively generating only 60 % of the corresponding borohydride salt, with the balance of the material sequestered as the esterbound Lewis acid-base adduct 3 a. Formation of the Lewis acid-base adduct could be minimized by increasing the steric bulk about the ester groups as in 1 d. The connectivity of the carbonylbound adduct was confirmed by an Xray crystallographic analysis of 3 e the product of the reaction of methyl ketone 1 e with BA C H T U N G T R E N N U N G (C 6 F 5 ) 3 . We also explored the generation of these pyridinium salts by employing frustrated Lewis pair methodology.…”

“…Abstract: We report herein that the reaction between a series of Hantzschs ester analogues 1 a-d with the Lewis acidic species BA C H T U N G T R E N N U N G (C 6 F 5 ) 3 results in facile transfer of hydride to boron. The main products of this reaction are pyridinium borohydride salts 2 a-d, which are obtained in high to moderate yields.…”

“…[15][16][17][18][19][20] In scattered examples, bulky amines have been shown to act as hydride donors [21] in reactions with BA C H T U N G T R E N N U N G (C 6 F 5 ) 3 via a C À H activation alpha to nitrogen [Eqs. (1)(2)(3)]. …”

“…This is particularly problematic for borohydrides destined for use in energy storage applications where cost effective reconstitution of the boron hydride is essential. [4,6] Other methods for hydride transfer to boron have included less reactive species such as R 3 SiH, [9] Bu 3 SnH, [10] and Rh hydrides, [14] although the use of these reagents on stoichiometric scale is prohibitive.…”

“…In organic chemistry, hydroboration and borohydride reagents that perform selective reductions as well as C À H functionalizations are critically important. [1][2][3] On the other hand, boron À hydride species such as ammonia borane [4][5][6][7] are of considerable interest as molecular hydrogen storage materials. Standard methods of borohydride synthesis involve the use of inorganic hydrides such as sodium hydride.…”