From boron-stabilized carbanions

See also Borates Boric acid Sodium borates boron oxides, 4 246-249 boron oxides table,4 242t environmental concerns, 4 284—285 health and safety factors, 4 285-288 occurrence, 4 245—246 Boron perchlorates, 18 278 Boron phosphate, 4 242t, 283 Boron removal, from water, 14 418 Boron-stabilized carbanions, 13 660-661 Boron subhalides, 4 141 Boron suboxide, 4 242t Boron tribromide, 4 138 manufacture, 4 145—146 physical properties of, 4 139-140t, 325 reactions, 4 141 specifications, 4 147t uses of, 4 149 Boron trichloride, 4 138 manufacture, 4 145—146 physical properties of, 4 139-140t reactions, 4 141... 

If the pKa of the corresponding acid R1 - H from the stabilized carbanion is smaller than 35, the migration of R1 fails in (dichloromethyl)borate complexes. Failure to convert pinanediol [(phenylthio)methyl]boronate to an a-chloro boronic ester has been reported15. Reaction of (dichloromethyl)lithium with an acetylenic boronic ester resulted in loss of the acetylenic group to form the (dichloromethyl)boronate, and various attempts to react (dichloromethyl)boronic esters with lithium enolates have failed17. Dissociation of the carbanion is suspected as the cause, but in most cases the products have not been rigorously identified. 

Although cleavage of gem-diboryl compounds is a mild and general process for die production of boron-stabilized carbanions, it nevertheless suffers from two disadvantages. Firstly, although... 

Boron-stabilized carbanions may also be produced by selective cleavage of a heteroatom group from an a-substituted organoborane such as a borylstannylmethane (equations... 

Matteson and coworkers have described the deprotonation and alkylation of bis(l,3,2-dioxaborin-2-yOmethane (11). Deprotonation with LiTMP yields the stabilized anion, which can be alkylated with a variety of primary alkyl halides. Oxidation under basic conditions then unmasks the carbonyl group. Matteson has also described the deprotonation of some substituted boronic esters (12 X = SPh, SiMei). - The alkylated products derived from (12 X = SPh) can be treated with A/-chlorosuccinimide under mild basic conditions to yield either the monothioacetals or the acetals. Boron-stabilized carbanions can also be generated by transmetallation of the organostannanes. ... 

Boron-stabilized carbanions. Ordinarily bases coordinate with the boron atom of organoboranes. However, Rathke and Kow report that a highly hindered lithium amide such as lithio-2,2,6,6-tetramethylpiperidine or lithio-t-butylneopentylamine2 can remove the a-proton from an organoborane to generate carbanions. Thus treatment of the boron compound B-methyl-9-borabicyclononane (1)J in benzene with the former base for 12 hr. at room temperature followed by quenching with deuterium oxide results in deuterium incorporation of 50% (equation I). 

The monohydroboration of terminal alkynes with dicyclohexylborane, disiam-ylborane, catecholborane, and dimesitylborane, and complexes of dihaloboranes and 9-BBN provides the simple and efficient route to fra s-vinylboranes [1,2]. Unlike other dialkyl(vinyl)boranes, vinyl-9-BBN derivatives exhibit remarkable stability [3, 4]. However, with 1 1 stoichiometry of terminal alkyne 9-BBN, 9-BBN adds twice to give a significant amount of diboryl adduct (Eq. 5.19) from which boron stabilized carbanion can be made [5, 6]. The partial solution to dihydroboration is achieved either by employing 100% excess of the alkyne [3] or using silylated derivatives [4e, h]. 

Corey et al have elegantly exploited the ability of oxime ethers to stabilize carbanions syn to the N-alkoxy substituent in the boron trifluoride mediated addition of the mixed cuprate reagent derived from (177) to a,3-unsaturated oxime ether (178 Scheme 34). Stereochemistry is established by the ring r-bu-tyldimethylsiloxy group. The addition does not occur in the absence of boron tiifluoride. The alkylation of the cuprate adduct of (178) by iodoalkyne (179) provides the PGEj skeleton. 

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