Organoboron compounds in organic synthesis. 1. Asymmetric hydroboration

Asymmetric Hydroboration of 1,1‐Disubstituted Alkenes

“…They usually give good to high enantioselectivities with a broad range of alkenes (Table 1, columns 2 and 3). [3] Whilst Masamunes C 2 -symmetric borane (2,5-dimethylborolane, DMB) gives higher enantioselectivities in the majority of cases (Table 1, column 4), [4] its lengthy synthesis (7 steps) detracts from the practicality of using this reagent relative to that of Browns.…”

“…Indeed, achieving high enantioselectivity in the transformations of 1,1-disubstituted alkenes represents the ultimate challenge in asymmetric synthesis. (H. C.) Browns hydroboration [4] and (J. M.) Brown-Hayashis rhodium-catalyzed hydroboration…”

“…[4,10] However, it is in the hydroboration of 1,1-disubstituted alkenes that Soderquists reagents really stand out (Table 1, rows 4 and 5 and Table 3). Whereas previously enantioselectivities rarely rose above 10 % ee, the new reagents give up to 92 % ee.…”

Asymmetric hydrogenation of 1-phenylethenylboronic acid and esters for the synthesis of chiral organoboron compounds

“…Chiral organoboron compounds [1] are available from the hydroboration of internal alkenes with chiral hydroboration reagents including di(isopinocampheyl)borane [2], mono-isopinocampheylborane [2], and 2,5-dimethylboronane [3]. The discovery of the intramolecular S N 2 substitution reaction of chiral (α-haloalkyl)boronic esters with carbon-or hetero-nucleophiles has resulted in an additional and practical method of broad scope [4].…”

Allylation of Ketones with a Ferrocene‐Based Planar Chiral Lewis Acid

“…[8,9] We converted 1-Cl to the methoxy derivative 1,2-Fc(BMe(OMe))-(SnMe 2 Cl) (1-OMe) and treated the latter with 0.5 equivalents of (1R,2R)-(À)-N-methylpseudoephedrine ((À)-MPE) or (1S,2S)-(+)-N-methylpseudoephedrine ((+)-MPE, Scheme 1). [10,11] The crude product was extracted with hexanes, and the chelate complexes (R p )-2-(À)-MPE and (S p )-2-(+)-MPE were isolated from the corresponding solid fractions; the characteristics of the (S p )-2-(+)-MPE enantiomer are described below, and similar considerations apply to the R p isomer.…”