Esters from organoboranes

ESTERIFICATION OF HINDERED ALCOHOLS tert-BUTYL p-TOLUATE, 51, 96 Esters, from diazoketones and organoboranes, 53, 82 Esters, a-deuterio-, 53, 82 Esters, y [Pg.59]

The electrochemical reaction of organoboranes in the presence of propenoic acid esters has been reported to be a convenient synthesis of carboxylic esters while with acetone, trialkylboranes react electrochemically to yield dioxaboro-lanes (6) and dioxaborinanes (7) [reaction (3)]. The first direct synthesis of carboxylic acids from organoboranes has been published and involved the reaction of trialkylboranes and the dianion of phenoxyacetic acid in THF [reaction (4)]. ... 

Reactions.—A variety of interesting and useful syntheses have been published involving the reaction of dimsyl anion [MeS(0)CHa ] with esters and lactones,with disulphides, with chlorosilanes, with sulphinate esters, with organoboranes, and with stilbenes. Simple and functionalized a-sulphinyl carbanions can be condensed with carbonyl compounds or alkylated, often in a stereocontrolled manner, as in a nicely conceived synthesis of biotin. Considerable attention has been given to methods for the removal of the sulphoxide function following carbon-carbon bond formation. Among the methods used are reduction by aluminium amalgam (with j3-keto-sulphoxides), reduction with Raney nickel, pyrolytic elimination of sulphenic acid, elimination of sulphur dioxide from sultines, e.g. (64), and sulphoxide-... 

The main chemical products produced from these minerals are (a) boron oxides, boric acid and borates, (b) esters of boric acid, (c) refractory boron compounds (borides, eu .), (d) boron halides, (e) boranes and carbaboranes and (f) organoboranes. The main industrial and domestic uses of boron compounds in Europe (USA in parentheses) are ... 

Sulfonylhydroxylamines and hydroxylamine O-sulfonic acid have found wide apph-cation in synthesis of amines from achiral or chiral organoboranes and boronate esters and the hydroboration-amination methodology is successfully used for direct amination of alkenes. 0-Sulfonyloximes were also found to be good reagents for synthesis of amines from organomagnesium, -copper and -zinc reagents. 

Synthesis of pure enantiomers. Brown and Singaram1 have reviewed the chiral organoboranes obtained from (+)- and (- )-pinene and their use for synthesis of optically pure amines, halides, hydrocarbons, lithium alkylborohydrides, ketones, aldehydes, a-chiral acids, esters, nitriles, alkynes, and alkenes. 

As a synthetic route, this organoborane synthesis parallels the aoetoaoetic ester and malonic ester syntheses. An acetone unit is furnished by acetoacetic ester or, here, by bromoacetone an acetic add unit is furnished by malonic ester or, here, by bromoacetic ester. In these syntheses, bromine plays the same part that the —COOEt group did by increasing the acidity of certain a-hydrogens, it determines where in the molecule reaction will take place it is easily lost from the molecule when its job is done. Unlike the loss of —COOEt, the departure of —Br is an integral part of the alkylation process. 

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