Boranes optical resolution

P-Chiral phosphine-borane compounds were synthesized through lipase-catalyzed optical resolution (Figure 17 (d)).18e Alkyl(l-hydroxymethyl)phosphine-boranes (up to ee 99% ) were obtained using lipase AK or CAL. 

Shioji K, Kurauchi Y, Okuma K (2003) Novel synthesis of P-chiral hydroxymethylphosphine-boranes through lipase-catalyzed optical resolution. Bull Chem Soc Jpn 76 833-834... 

Asymmetric hydroboration.1 Hydroboration of 1-phenyl-1-cyclopentene with IpcBH2 (100% ee) results in a dialkylborane (1) containing the traws-2-phenylcyclopentyl group of 100% ee. However, hydroboration of prochiral trisubstituted alkenes usually results in alkylisopinocampheylboranes of 50-85% ee. Most of these products are solids, and selective crystallization (usually from ether) can give the optically pure dialkyboranes. In some cases resolution can be achieved by allowing the impure borane to age for several... 

A very important feature of the monoalkylmonoisopinocampheyl boranes obtained from prostereogenic alkenes is their tendency to crystallize from the reaction mixture. This crystallization process is an efficient resolution technique providing crystalline material of high optical purity. Utilizing this technique, chiral alcohols of essentially 100% ee can be prepared by the hydroboration of prostereogenic, A -disubstituted and trisubstituted alkenes with monoisopinocampheylborane71, 73. 

The synthesis consisted of the reaction of 90 with N-bromosuccinimide (NBS) to give the bromolactone 91, substitution of the bromine atom for a hydroxyl group to form 92 and reduction of the lactone grouping in 92 with bis[2-(3-methylbutyl)] borane to give the desired product. Optic ly active forms of the acid 90, which served for the synthesis of enantiomeric 2-deoxy-erythro-pentoses, were readily obtained by resolution of the racemate with quinine. 

Di(isopinocampheyl)borane Resolution of racemic ethylene derivatives with optically active boranes s. 19, 720 Lithium tetrahydridoborate s. under (C2H )gN,HCl Sodium tetrahydridoborate/boron fluoride Boranes from ethylene derivatives s. 16, 753... 

An alternative means of resolution depends on the differences in rates of reactions of enantiomers with a chiral reagent. The transition state energies for reaction of one chiral molecule with another can be different for each enantiomer. If a racemic mixture R molecule -h 5 molecule) reacts with an optically active reagent (R reagent), the two transition states R molecule / reagent) and (5 molecule i reagent) bear a diastereomeric relationship to each other. Kinetic resolution is the term used to describe the separation of enantiomers by selective reaction with an optically active reagent. A very useful application of this technique is the resolution of allenes by preferential reaction of one enantiomer with an optically active borane. Hydroboration of the allenes occurs at different rates, and the reaction mixture becomes enriched in the less reactive enantiomer. An allene that has been partially resolved by this technique was presented as an example of an axially dissymmetric molecule in Scheme 2.1 68 entry 2,1,3-dimethylallene). ... 

Di(isopinocampheyl)borane Resolution of racemic ethylene derivatives with optically active horanes... 

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