Boron trimethyl, reaction

For example, Figure 2.3 shows plots of the a constants of X vs. log p/T of aliphatic carboxylic acids (XCOaH) and vs. log k for the dehydration of acetaldehyde hydrate by XC02H. Deviations from Equations 2.18 and 2.19 occurwhen the rate of reaction or position of equilibrium becomes dependent on steric factors. For example, Taft studied the enthalpies of dissociation, A Hd, of the addition compounds formed between boron trimethyl and amines (X1X2X3N) and found that when the amine is ammonia or a straight-chain primary amine the dissociation conforms to Equation 2.20, in which 2 ° is the sum of the a values for the... 

In Table 1, the heats of addition reactions are shown for four series of compounds. The first series (a) is for the reactions between boron trimethyl and either ammonia or the methylamines, and shows the steady rise in — /III values, along the series ammonia, methyl-amine, dimethylamine with a fall on passing from dimethylamine to trimethylamine. 

Air-Stable boron-containing polymers can be prepared by the reaction of dicyano compounds with the / fZ-butylborane—trimethyl amine complex (449). 

Because the breadth of chemical behavior can be bewildering in its complexity, chemists search for general ways to organize chemical reactivity patterns. Two familiar patterns are Br< )nsted acid-base (proton transfer) and oxidation-reduction (electron transfer) reactions. A related pattern of reactivity can be viewed as the donation of a pair of electrons to form a new bond. One example is the reaction between gaseous ammonia and trimethyl boron, in which the ammonia molecule uses its nonbonding pair of electrons to form a bond between nitrogen and boron ... 

The simplest type of Lewis acid-base reaction is the combination of a Lewis acid and a Lewis base to form a compound called an adduct. The reaction of ammonia and trimethyl boron is an example. A new bond forms between boron and nitrogen, with both electrons supplied by the lone pair of ammonia (see Figure 21-21. Forming an adduct with ammonia allows boron to use all of its valence orbitals to form covalent bonds. As this occurs, the geometry about the boron atom changes from trigonal planar to tetrahedral, and the hybrid description of the boron valence orbitals changes from s p lo s p ... 

Methyl cc-D-glucofuranosidurono-6,3-lactone (26) may be obtained exclusively by reaction of 4 with trimethyl orthoformate in the presence of boron trifluoride etherate.28 Its 2,5-dimethyl ether (27) is formed by methyl iodide-silver oxide methylation29,30 (Purdie-Ir-... 

The photolysis of trimethyl boron at temperatures up to 300 °C may occur by reactions (1)—(3) of the pyrolysis process112. Subsequent steps which lead to hydrogen formation in the pyrolysis system are much less important [CH4 H2 a 2 1 under pyrolysis conditions, 9 1 in photolysis system]. 

The analogous reactions of PbCl2 with lithium l-(dimethylamino)-3,5-dimethylboratabenzene or l-[bis(trimethyl-silyl)amino]-3,5-dimethylboratabenzene yield the corresponding sandwich compounds 44 and 45. The lead atom of 45 displays a rather asymmetric bonding to the boratabenzene rings as evidenced by the fact that the lead-to-carbon/ boron distances span the large range from 2.519 to 3.033 A.7... 

A boron analog - sodium borohydride - was prepared by reaction of sodium hydride with trimethyl borate [84 or with sodium fluoroborate and hydrogen [55], and gives, on treatment with boron trifluoride or aluminum chloride, borane (diborane) [86. Borane is a strong Lewis acid and forms complexes with many Lewis bases. Some of them, such as complexes with dimethyl sulfide, trimethyl amine and others, are sufficiently stable to have been made commercially available. Some others should be handled with precautions. A spontaneous explosion of a molar solution of borane in tetrahydrofuran stored at less than 15° out of direct sunlight has been reported [87]. 

Although the allylation reaction is formally analogous to the addition of allylboranes to carbonyl derivatives, it does not appear to occur through a cyclic transition state. This is because, in contrast to the boron in allyl boranes, the silicon in allylic silanes has no Lewis acid character and would not be expected to coordinate at the carbonyl oxygen. The stereochemistry of addition of allylic silanes to carbonyl compounds is consistent with an acyclic transition state. Both the E- and Z-stereoisomers of 2-butenyl(trimethyl)silane give the product in which the newly formed hydroxyl group is syn to the methyl substituent.64 The preferred orientation of approach by the silane minimizes interaction between the aldehyde substituent R and the methyl group. 

Several nonreductive methods for cleavage of benzyl groups have also been developed. Treatment with s-butyllithium, followed by reaction with trimethyl borate and then hydrogen peroxide, liberates the alcohol.24 The lithiated ether forms an alkyl boronate, which is oxidized as discussed in Section 4.9.2. 

Reaction 17 resembles the displacements on phosphorus discussed earlier, except that since trialkyl borons are electron deficient with only six electrons around boron, no valence-shell expansion is required. It appears to be a general reaction for boron and has been suggested by Matteson (15) to explain the conversion of trimethyl boroxine by tert-buty hypo-... 

The absence of an EPR signal in solution or in the solid state is indicative of a singlet ground state for the diradical ( BuBP Pr2)2- An indication of the radical character of this derivative is provided by a variety of facile oxidative addition reactions (Scheme 9.12). " For example, the treatment of ( BuBP Pr2)2 with diphenyl diselenide (or elemental selenium) produces a bicyclic compound in which a selenium atom bridges the two boron atoms. Trimethyl tin hydride reacts rapidly with ( BuBP Pr2)2 to give the trans adduct. Finally, ( BuBP Pr2)2 is slowly oxidised by deuterated chloroform to produce a R,R -dichloro adduct as a mixture of cis and trans isomers. 

Heteroatoni groups such as boron or silicon can activate or direct synthetic reactions. Use of such activation has become of major importance in organic syntheses. Examples in this volume are BORANES IN FUNCTIONALIZATION OF DIENES TO CYCLIC KETONES BICYCLO[3.3.1]NONAN-9-ONE and BORANES IN FUNCTIONALIZATION OF OLEFINS TO AMINES 3-PINANAMINE. Use of trimethylsilyl or trimethyl-silyloxy groups to activate a 2-butenone or a butadiene are illustrated by the preparations 3-TRIMETHYLSILYL-3-BUTEN-... 

Reaction of 2-cyanomethyl-4H-l,3-benzothiazin-4-one with benzoylace-tonitrile at 160°C yielded 8-cyano-7-imino-9-phenyl-7//,ll//-pyrido[2,l-6][l,3]benzothiazin-l 1-one (85MI1 86MI2). Reaction of 2-ethoxy-2,3 dihydro-4//-l,3-benzothiazin-4-one with 1,2,3,4-tetramethylbutadiene and 2,4-dimethyl-l,3-pentadiene in the presence of boron trifluoride in diethyl ether gave rise to 6,7,8,9-tetramethyl- and 7,9)9-trimethyl-5a,6,9,ll-tetrahydropyrido[2,l-6][l,3]benzothiazin-ll-one, respectively (73JHC149). 

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