Cyclic dialkoxyboranes

No report was found on a good yielding distillation of HBnpg. Solutions of HBnpg have been prepared and used in situ although the reagent exhibits poor purity ( H NMR), it can be used in an efficient Ni-catalyzed borylation of aryl halides. i  

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Long-range mediation by achiral boronate (IJ-asymmetric induction) in ketone reduction by borane is feasible. Enantioselective reduction of imines with stoichiometric quantities of a cyclic dialkoxyborane prepared from tartaric acid has been reported. 

The cyclic dialkoxyborane 4,4,6-trimethyl-l,3,2-dioxaborinane (HBhg), the vinylboronic ester 2-ethenyl-4,4,6-trimethyl-l,3,2-dioxaborinane (vinylBhg) and the alkynylboronic ester 2-ethynyl-4,4,6-trimethyl-l,3,2-dioxaborinane were first reported in 1966-67 by Woods and coworkers. The authors stressed the high stability of HBhg towards disproportionation, as compared to the parents 1,3,2-dioxaborinane and 1,3,2-dioxaborolane, and its potential for the hydroboration of alkynes. In addition, the first reported o-metal-boron bond (rhodium) was prepared from HBhg. ... 

Cyclic dialkoxyboranes are best prepared by reaction of the diol with dibo-rane or a BH3 complex. The problematic side-reaction is disproportionation (Scheme 3.3). It is particularly fast for the parent dioxaborolane [n = 1), which... 

In a study on an enantioselective version of rhodium-catalyzed hydroboration of alkenes the influence of the nature of the hydroboration agent was studied in detail. Twelve cyclic dialkoxyboranes, including catecholborane... 

Non-aromatic Boron Heterocyclics.—The range of cyclic dialkoxyboranes derived from monosaccharides has been extended to cover deoxyaldohexoses [by treatment of the sugar with ethyl(dimethoxy)borane] and derivatives of glucose (by a novel reduction process). If two dioxaborolane units are appropriately disposed in space, exchange of alkoxy groups between boron atoms is possible, as for example in the equilibration of compounds (17) and (18). ... 

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