Borane, derivatives chloro

Advances in the use of anionic stereogenic phosphorus have been interesting. Acylation of lithium o-anisylphenylphosphide with chloro-formates bearing chiral alkyl groups provided a diastereomeric mixture that could be induced to undergo an inversion at phosphorus (at relatively low temperature) to form the more favorable diastereoisomer in a crystalline lattice.186 Subsequent conversion to the quaternary phos-phonium species was followed by removal of the acyl group and isolation of the chiral tertiary phosphine as the borane derivative (Equation 3.10). 

Benzylic halides are reduced very easily using complex hydrides. In a-chloroethylbenzene lithium aluminium deuteride replaced the benzylic chlorine by deuterium with inversion of configuration (optical purity 79%) [537]. Borane replaced chlorine and bromine in chloro- and bromodiphenylme-thane, chlorine in chlorotriphenylmethane and bromine in benzyl bromide by hydrogen in 90-96% yields. Benzyl chloride, however, was not reduced [5iSj. Benzylic chlorine and bromine in a jy/n-triazine derivative were hydrogeno-lyzed by sodium iodide in acetic acid in 55% and 89% yields, respectively [5i9]. 

More recently, several groups prepared related methylene-bridged PBs by reacting R2PCH2Li derivatives (R = Me, Ph, f-Bu) with chloro-boranes... 

Because they serve as versatile starting materials for a variety of other boranes, the dihalo boranes, particularly the fluoro and chloro derivatives, are the most important members of this class of compounds. Their chemistry, along with other pentafluor-ophenyl boron halides, has been reviewed recently from a personal perspective by Chi vers,15 whose PhD thesis described early explorations into the chemistry of these compounds. Most of the known literature on these compounds deals with pentafluor-ophenyl compounds, but the chemistry is likely extendable to other compounds with different AiF groups. 

Fu and co-workers have shown that the l-chloro-boracyclohexa-2,4-diene 97 reacts with 4-phenylpyridine at room temperature to provide the />-terphenyl analog 26 in 76% yield as an early example of a borabenzene-pyridine-type complex (Equation 6). The X-ray structure of 26, discussed in Section 7.14.3, shows the three rings not to be coplanar <1997OM1501>. Exposure of the l-chloro-boracyclohexa-2,4-diene 98 to a stabilized carbene results in formation of the complex 29 in 83% yield as an air- and moisture-sensitive colorless powder (Equation 7), crystals of which were grown from toluene the X-ray structure of 29 has been discussed in Section 7.14.3. The use of bulky lithium bases to deprotonate the bis(amido) or bis(alkoxy)boranes 19 allows for the formation of the dianionic 2,2 -diboratabiphenyl derivatives 20 (X = NHPh, OBn), the solid-state structures of which have been discussed (Equation 8) <2006CJC81>. 

Cyclopropenylium ions 1 were converted into the corresponding cyclopropenes 2 by the addition of hydride ion derived from various hydride sources, such as lithium aluminum hydride,sodium borohydride, borane-amine complex, triethylsilane, and tributyl-tin hydride. Particularly in the case of borohydride reduction of the diphenylcyclo-propenylium ion, the order of reagent addition was quite important. The slow addition of an acetonitrile solution of the cyclopropenylium salt into a solution of the borohydride gave the cyclopropene derivative,whereas the inverse order of addition resulted in quantitative formation of 1,2,4,5-tetraphenylbenzene (see Section 2.1.2.3.), No such precaution of the inverse addition was required in the case of borane-amine reduction of the l-chloro-2,3-diphenyl-cyclopropenylium ion. ... 

Reactions of Enamines.—Hydroboronation of the 2-enamine (397) gave a product (amine-borane adduct ) from which the 3a- and 3 -pyrrolidino-derivatives (398 3a 3)5 = 82 18) were liberated by refluxing methanol. The stereochemistry of this reduction is quite unusual, and not fully explained. Reaction of the 3,5-dienamine (399) with dichlorocarbene led to ring expansion, giving the A-homo-4-chloro-dienone (400). " Condensations of the enamine... 

Simple benzo[6]borolanes (or boraindanes) such as the 1-chloro derivative (79) have been synthesised by flash vacuum pyrolysis of dichloro(2-ethylphenyl)borane (78) (Equation (16)) <87AG(E)665, 87CB1331). 

The stereoselective synthesis of the (RJi)- (or (S,S)-ligands) 99 was performed in several steps using the ephedrine methodology with (-t)- or (—)-ephedrine, respectively. The key step of the synthesis is the methano bridge formation by reaction of the carbanion derived methyl phosphine borane 98 with the chloro... 

Phospholanes usually adopt a folded envelope configuration, with which there are possible alternative arrangements (6.816). Phospholane, (CH2)4PH, mp = -88°C, bp = 100-103 C, can be prepared via the dimethylamine borane adduct or the chloro derivative. 

Diphenylcyclopropene may be made either by dehydrochlorination of l chloro-1,2-diphenyl cyclopropane,or by reduction of the chlorodiphenyl-cyclopropenium ion with trimethylamine-borane in the presence of DMF. Although derivatives of cyclopropenone have been isolable as pure compounds for a number of years, the parent compound has been known only in solution until recently. It has now been purified and shown to have an unusually high b.p. (30 C, 0.45 Torr). It is stable only below its m.p. (—29 to —28°C) and polymerizes at room temperature. 

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