Enantioselective diborations, 1,3-dienes

The last cascade reaction we report here for the synthesis of a quaternary spirocenter employs a platinum catalyst [21 ]. A regio and enantioselective diboration of 1,3-diene 44 could lead to a chiral bis(boryl) intermediates 45 (Scheme 9.12), which could then react in two subsequent asymmetric carbonyl allylations of succinic dialdehyde, leading to the creation of three stereogenic centers in good diastereomeric (9 1) and promising enantiomeric ratios (88 12) 46. 

This interest in catalytic hydroboration led to the development of the transition-metal-catalyzed diboration of alkenes and alk5mes. The diboration of alkenes and alkynes generates bifunctional products, and additions to alkenes have now been conducted with high enantioselectivity. The following sections describe the t es of catalysts used for catalytic hydroboration and diboration of alkenes, alkynes, and dienes, as well as catalytic cycles that accoimt for selectivities and side products formed during these processes. 

Palladium-catalyzed diboration can be achieved with bis(pinacolato)diboron for strained 1,2-disubstituted alkynes. ° Analogously, palladium-catalyzed addition reactions of diboron compounds provide 1,2-bisborylalkanes from l-alkenes ° or cis-l,4-bisboryl-2-alkenes from 1,3-dienes.2,3-Bisboryl-l-propenes are accessible from allenes (Scheme 5-174). The asymmetric allene diboration was examined by Burks et ai, who showed that monodentate phosphoramidite ligands gave excellent enantioselectivities (up to 97% ee) (Scheme 5-174). The (asymmetric) metal-catalyzed reactions of diboron, silylboron and disilane compounds have been reviewed.Recently, the addition across two triple bonds to give dienes has been explored by Singidi et... 

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