Trimethylaluminum-Lithium

A is approximately twice the observed covalent radius of lithium, and both the Li—C distance and the Li—C—Li angle are reminiscent of the trimethylaluminum structure previously described. In the two tetra-mers for which structural data are available, the Li—Li distances are substantially shorter in the range of 2.4 to 2.6 A with Li—C distances in the 2.2-2.5 A range. Crystallization effects may play a substantial role in the ethyllithium system since this compound is hexameric in noninteracting solvents but crystallizes in the tetrameric form. 

Stereoselective reaction with ketones. The reaction of ketone 1 with methyl-lithium, trimethylaluminum, and lithium letramethylaluminate shows no stcrco-specificity. The reaction with mcthylmagncsium bromide gives the two possible adducts in the ratio 2.4 1. The best stereospccificity is observed with dimethylsulf-oxonium methylide, which converts 1 into 2 and 3 in a ratio about 5 1. Reduction of the epoxides with lithium triethylborohydride gives the desired tertiary alcohols. This reaction was used in a synthesis of ( ) stemodin (4).2... 

Triethylaluminum, 204 Triisobutylaluminum, 205 Trimethylaluminum, 22, 205 Vilsmeier reagent-Lithium tri-r-butoxy-aluminum hydride, 342 Boron Compounds Alkyldimesitylboranes, 8 Allenylboronic acid, 36 9-Borabicyclo[3.3.1]nonane, 92 Borane-Dimethylamine, 42 Borane-Dimethyl sulfide-Sodium borohydride, 25... 

Selective cleavage of epoxides. The a- and /f-benzyloxy epoxides 1 and 3 (either cis or trans) undergo almost exclusive /(-addition with trimethylaluminum catalyzed by n-butyllithium or lithium methoxide to give the alcohols 2 and 4, respectively. The regioisomeric alcohols are formed only in traces. CHjMgBr, CH3Li, or (CH3)2Mg are much less selective.2... 

CLAISEN REARRANGEMENT Alkylaluminum halides. Lithium diisopropylamide. Potassium hydride. Sodium dithionite. Titanium(TV) chloride. Trifluoroacetic acid. Trimethylaluminum. 

Carbon-centered nucleophiles can also be used to advantage in the reaction with epoxides. For example, the lithium enolate of cyclohexanone 96 engages in nucleophilic attack of cyclohexene oxide 90 in the presence of boron trifluoride etherate to give the ketol 97 in 76% yield with predominant syn stereochemistry about the newly formed carbon-carbon bond <03JOC3049>. In addition, a novel trimethylaluminum / trialkylsilyl triflate system has been reported for the one-pot alkylation and silylation of epoxides, as exemplified by the conversion of alkenyl epoxide 98 to the homologous silyl ether 99. The methyl group is delivered via backside attack on the less substituted terminus of the epoxide <03OL3265>. 

There has been only a few reports on reactions of small rings with metal ynolates. Oxiranes are much less electrophilic than carbonyls and sometimes need activation by Lewis acids or Lewis-acidic organometals. The lithium-trimethylaluminum ate complex of i/ZyZ-substituted ynolate 105 reacts with the oxirane 106 to give the y-lactone 107 (equation 44), while lithium silyl-substituted ynolates are inert to oxiranes. There have been no reports using carbon-substituted metal ynolates. 

Nucleophilic addition of alkyl lithium to difluorovinyl-substituted epoxide (48) proceeds on the difluoromethylene carbon via the addition-ring opening pathway [16]. However, trimethylaluminum reagent transfers the methyl group at the carbon remote from the difluorinated carbon of 50 presumably via the Lewis acid catalyzed ring opening-addition mechanism as shown in Scheme 2.26. 

Disubstituted tetrahydropyridines16 have been reduced diastereoselectively by lithium aluminum hydride/trimethylaluminum. 

Enantiomerically pure (3.S)-6,8-dimethoxy-1,3-dimethyldihydroisoquinoline was reduced with lithium aluminum hydride/trimethylaluminum to give (l.S .3.S )-6,8-dimethoxy-l,3-dimethyltetrahydroisoquinoline with high diastereoselectivity (de 92%) in 85% yield. 

ARTIC (74-87-3) Flammable gas (flash point <32°F/<0 C). Moisture causes decomposition. Violent reaction with strong oxidizers, acetylene, anhydrous ammonia, amines, fluorine, interhalogens, magnesium, potassium, sodium, zinc, and their alloys. Reacts with barium, lithium, titanium. Contact with powdered aluminum or aluminum chloride forms pyrophoric trimethylaluminum may cau.se ignition or explosion. Attacks plastics, rubber, and coatings. 

CONJUGATE ADDITIONS Bis(methylthio)(trimethylsilyl)methyllithium. Diethylalum-inum cyanide. Di(a-methoxyvinyl)copperlithium. Ethyl diethoxyacetate. Ethyl methylsulfinylacetate. Lithium a-carboethoxy vinyl(l-hexynyl)cuprate. Potassium fluoride. Quinine, chinchonine. Titanium tetrachloride. Trimethylaluminum. Tris-(phenylthio)methyllithium. 

The few crystal structures obtained from aluminum enolates that are less important in synthesis than their boron counterparts reveal dimeric aggregates (Scheme 3.5). This maybe illustrated by the enolates 15 [43a], obtained fromiV,Af-dimethyl methyl glycinate through transmetallation of the lithium enolate, and 16 [43b] that was prepared by direct enolization of 2,4,6-trimethylacetophenone and trimethylaluminum. Both dimers feature an AI2O2 core unit and clearly demonstrate the O-bound character of aluminum enolates. 

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