Suzuki Miyaura chiral biaryls

Using other chiral 1,2-diols such as 1,2-diphenyl-1,2-ethanediol or 2,3-butanediol, the Lipshutz approach allows to rich very high diastereoselectivity [19]. Among reactions that have been used in the diastereoselective synthesis of unsymmetrical axially chiral biaryls, beside Ullmann and Lipshutz reactions, are the Suzuki-Miyaura and Meyers synthesis of biaryls. 

Diastereoselective version of the Suzuki-Miyaura reaction was accomplished using planar chiral tricarbonylchromium-complexed aryl bromide with arylboronic acids to form the respective biaryls with very high diastereomeric excess (d.e.) For example, compound 582 underwent the Suzuki-Miyaura reaction with boronic acid 583 to give the biaryl 584 in 88% yield [20], Scheme 7. 

However, in the Suzuki-Miyaura reaction of relatively simple, enantiomerically pure, both naphthyl bromides and naphthylboronic acids gave diastereomeric mixtures, indicating rather low diastereoselectivity [21]. More important access to axially chiral biaryls is the Meyers approach in its diastereoselective version [22-25]. It was foimd that oxazolines, derived from readily available amino alcohol 585 [22], underwent the Meyers synthesis of biaryls giving the expected biaryls in high d.e. s [23-25]. Thus l-methoxynaphthyl-2-carboxamide (586) was activated with triethyloxonium tetrafluoroborate to 587, which reacted with 585 to give the oxazoline 588. The latter... 

Enantioselective synthesis of axially chiral biaryls include all approaches where the starting material is achiral and the chirality is induced by an influence of chiral catalyst or reagent. Among enantioselective reactions that have been successfully used in the synthesis of axially chiral biaryls are the Kharasch reaction [34-36], Suzuki-Miyaura reaction [37,38], oxidative phenolic coupling mediated by copper complexes... 

The enantioselective Suzuki-Miyaura reaction (SM) can be accomplished by using the chiral ligands 213 [37] or 631 [38], whose palladium complexes catalysed the crosscoupling reaction of sterically hindered iodides and bromides with also quite encumbered arylboronic acids furnishing the axially chiral, sterically demanded biaryls in moderate to good yields with low to moderate enantioselectivity. 

Total syntheses of vancomycin aglycone have been reported by outstanding synthetic teams [46-48], all of whom encountered stereoselective cOTistructiOTi of the axially chiral A-B biaryl ring system as an essential problem. One of the most efficient solutions to this problem was reported by Uemura et al. [49-51], and comprises the use of a planar chiral arene chromium complex in the Suzuki-Miyaura cross-coupling reaction. 

Before embarking on a more detailed discussion of this approach, let us first consider other chiral variants of the Suzuki-Miyaura reaction in the synthetic approach to enantiopure biaryls XVII (Scheme 5.5). 

In spite of some of the drawbacks mentioned in Sect. 5.3 of this chapter, the Suzuki-Miyaura reaction is certainly the most widely used method for stereoselective construction of the central bond in biaryls. This method can be classified into diastereoselective a and b) or enantioselective (c) variants (Scheme 5.5). The former two characterize chiral information present in one of the reacting partners, XV or XVI. In case a, this involves planar-to-axial induction of chirality from XV to XVII, while in case b, central-to-axial chirality is induced from XVI to XVn. The enantioselective method c involves two achiral partners XVIII and XIX, while the chiral ligand in the palladium complex contributes chiral information to the reacting system. 

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