2-Naphthylboronic acid

The success of the asymmetric aryl transfer from boronic acids also relied on another important phenomenon. The presence of catalytic amounts (10 mol%) of DiMPEG (MW = 2000) increased the enantioselectivity of the process significantly [49]. For example, without DiMPEG the reaction between benzaldehyde 37b and 1-naphthylboronic acid 40c gave the corresponding diarylmethanol 27g with 31% ee in 56% yield, whereas in the presence of the polyether, 27g was obtained in 85% ee and 91% yield (Scheme 2.1.2.12) [49]. 

The bromo derivative of A -mcthylsuccinimide did also undergo Suzuki coupling when treated with naphthylboronic acid in the presence of palladium acetate, triphenylphosphine and potassium carbonate (6.3.). The coupled product was deprotected under the reaction conditions and an indole derivative was isolated in good yield, which was successfully converted into the hexacyclic naphthopyrrolo[3,4-c]carbazole structure. Using the analogous trimethylstannyl-naphthalene derivative and optimised Stille coupling conditions the desired product was isolated only in 56% yield.5... 

Various arylboronic acids having o-, m-, and p-substituents smoothly underwent the addition to benzyl crotonate (7e) with high yields and high %ee (entries 5-11). There is no appreciable difference in yields and %ee between m- and p-functionalized arylboronic acids. The presence of o-substituent slightly retarded the addition due to its steric hindrance (entries 10 and 11) and the methoxy group again diminished the %ee (entry 11). The addition of 4-methylphenylboronic acid and 1-naphthylboronic acid to 7g resulted in 48 and 1 l%ee, respectively (entries 12 and 13). 

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... 

Scheme 6.28 Asymmetric Pd-Pymox-catalyzed arylation of an aldimine with 2-naphthylboronic acid,...

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