Borane carbonyls reactions with

Two sterically hindered /V-sulfonylated aminobomeols 42 were prepared from camphorquinone 11 and used after esterification for the formation of enolates which are alkylated or oxidized diastereoselectively (Sections D.1.1.1.3.2., D. 1.5.2.1., D. 1.5.2.3. and D.4.I.). The synthesis of these auxiliaries involves the reaction of camphorquinone 11 with 3,5-dimethylaniline to give the mono-imine by reaction with the sterically less hindered carbonyl group, followed by reduction with boranate and reaction with benzenesulfonyl chloride to give the exo.exo-product. or initial reduction with zinc/potassium hydroxide, then sulfonylation, and finally reduction with boranate to give the endo,endo-isomer21. 

Reactions of Organoborates. Scheme 9 reveals a fundamental synthetically useful difference between the 3-migration cyanoborate and borane carbonylation reactions.The thermodynamically more stable cyanide adduct is formed prior to electrophile-induced migrations, in contrast to the kinetically determined product resulting from carbonylation. Carbonylation of R3B in the presence of LiAlH(OMe)3 followed by treatment with acid and oxidizing agent is a particularly mild method for the preparation of secondary carbinols. ... 

Besides direct reduction, a one-pot reductive amination of aldehydes and ketones with a-picoline-borane in methanol, in water, and in neat conditions gives the corresponding amine products (Scheme 8.2).40 The synthesis of primary amines can be performed via the reductive amination of the corresponding carbonyl compounds with aqueous ammonia with soluble Rh-catalyst (Eq. 8.17).41 Up to an 86% yield and a 97% selectivity for benzylamines were obtained for the reaction of various benzaldehydes. The use of a bimetallic catalyst based on Rh/Ir is preferable for aliphatic aldehydes. 

Reaction of an alkylborane with a-halocarbonyl compounds in the presence of a base leads to the replacement of the halogen atom in the carbonyl compound with an alkyl group from the borane. The reaction is most commonly applied to a-bromoesters (Equation B3.18). 

The dialkenylchloroboranes undergo the usual reactions of vinylic boranes, e.g., protonolysis with acetic acid gives olefins, oxidation with alkaline hydrogen peroxide provides the corresponding carbonyl compounds. However, the most useful reactions of these compounds are their ready conversion to the stereochemically pure (E, Z)-1,3-dienes by the Zweifel reaction with I2-NaOH 37>107.108> and into the symmetrical (E,E)- 1,3-dienes, 09 0), mono-olefins 1U) and 1,4-dienes (Chart 10). 

Crotyl silanes offer the possibility of diastereoselectivity in reactions with aldehydes in the same way as the corresponding boranes. The mechanism is completely different because crotyl trialkylsilanes react via an open transition state as the silicon is not Lewis acidic enough to bind the carbonyl oxygen of the electrophile. Instead, the aldehyde has to be activated by an additional Lewis acid or by conversion into a reactive oxonium ion by one of the methods... 

Diselenoacetals are also useful for the protection or umpolung of the carbonyl group. - Bis(al-kylseleno)alkanes and arylseleno analogs are prepared by the reaction of carbonyl compounds with sele-nols and trimethylsilyl selenides in the presence of acid catalysts (cone. HCl, cone. H2SO4, Lewis acids such as BP3 Et20, TiCU, ZnCh or AICI3) or with tris(methylseleno)borane in the presence of LAH and BF3Et20.274... 

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