Cobalt carbonyl catalyzed reaction of tetrahydrofurans with a hydrosilane and carbon monoxide. A new reaction pathway leading to enol silyl ethers.

Cobalt carbonyl catalysed reaction of tetrahydrofurans with HSiEt₂Me and CO (1 atm) took a new reaction pathway leading to enol silyl ethers when acetonitrile was employed as the solvent.     

Silver-catalyzed formal inverse electron-demand Diels-Alder reaction of 1,2-diazines and siloxy alkynes

A highly effective silver-catalyzed formal inverse electron-demand Diels-Alder reaction of 1,2-diazines and siloxy alkynes has been developed. The reactions provide ready access to a wide range of siloxy naphthalenes and anthracenes, which are formed in good to high yields, under mild reaction conditions, using low catalyst loadings.     

Preparation and Diels-Alder chemistry of 4-vinylimidazoles

Various 4-vinylimidazole derivatives have been prepared from the corresponding 4-iodoimidazoles or from urocanic acid. Several methods for the elaboration of these vinylimidazoles and their Diels-Alder reactions are reported. All of the vinylimidazoles prepared in the course of this study react with N-phenylmaleimide quite readily with mild thermal activation providing a single cycloadduct, in most cases the initial, nonaromatic adduct. With more electron rich substrates, there is a tendency for these initial cycloadducts to undergo aromatization, ene reaction, and oxidation although this can be circumvented to a large extent by the choice of reaction conditions. Limited reactions were observed with other dienophiles, providing the expected cycloadducts in most cases, although an abnormal adduct was obtained in one case with dimethyl acetylene dicarboxylate. These substrates also participate in regioselective Diels-Alder reactions with monoactivated dienophiles, but require fairly forcing conditions, thus only providing the aromatized cycloadducts in modest yields. An investigation of substituent effects at the 2-position of the imidazole moiety was undertaken, in which electron-donating and weakly electron-withdrawing substituents are tolerated. In addition, several substrates with terminally substituted vinyl moieties have been investigated.     

Preparation of silyl derivatives of unsaturated carbocyclic compounds by the Diels-Alder reaction of 1,2-dimethylenecyclobutane and vinylsilanes

The Diels-Alder reactions of 1,2-dimethylenecyclobutane with vinyltrichlorosilane and vinylmethyldichlorosilane give the corresponding trichlorosilyl and methyldichlorosilyl derivatives of cyclobutene. Methylation of these derivatives gave 4-trimethylsilylbicyclo[4.2.0]oct-1-ene, which underwent thermal isomerization to 4-trimethylsilyl-1,2-dimethylcyclohexane.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 943–945, April, 1991.     

Azetidinyl ketone chemistry. C-Methylation reactions and stereostructure - spectra relationships

The C-methylation of the potassium salt of 1-t-butyl-2-phenyl-3-(p-phenylbenzoyl)azetidine ( 1a ) with methyl iodide was studied in three solvents, and the stereochemical outcome of the reaction was shown to be dependent upon the solvent used. These results are rationalized in terms of the probable relative rates of the reaction in the various solvents and/or the effect of solvent on the structure of the anionic intermediate. Similar treatment of the potassium salt of 1-t-butyl-2-phenyl-3-benzoylazetidine ( 3a ) in ethyl ether gave a comparable result. The configurations of the epimeric C-methyl products ( 2a and 2b , and 4a ) were assigned on the basis of their spectral properties. With the aid of spectral data for a model compound, l-t-butyl-3-benzoyl-azetidine ( 5 ), several stereostructure-spectra relationships for 3-azetidinyl ketones are presented.     

The indium(III) chloride-catalysed hydrolysis and in situ Mukaiyama-type reaction of arylmethyl ketone derived silyl enol ethers under solvent-free conditions

Treatment of trimethylsilyl enol ethers of arylmethyl ketones with catalytic amounts of indium(III) chloride under solvent-free conditions leads to a remarkably efficient process of in situ hydrolysis and Mukaiyama-type addition to the resulting ketones.     

Diastereoselective Diels-Alder reactions of N-sulfonyl-1-aza-1,3-butadienes with optically active enol ethers: an asymmetric variant of the 1-azadiene Diels-Alder reaction

The first detailed study of a room-temperature asymmetric Diels-Alder reaction of N-sulfonyl-1-aza-1,3-butadienes is reported enlisting a series of 19 enol ethers bearing chiral auxiliaries, with many providing highly diastereoselective (endo and facial diastereoselection) reactions, largely the result of an exquisitely organized [4+2] cycloaddition transition state. Three new, readily accessible, and previously unexplored auxiliaries rationally emerged from the studies and provide remarkable selectivities (two of these give 49:1 endo:exo and 48:1 facial selectivity) that promise to be useful in systems beyond those detailed.     

Intramolecular Diels-Alder reaction leading to tricyclic derivatives as intermediates of natural products synthesis

Tricyclic compounds 4a and 4b possessing a bicyclo[4.3.0] moiety, were successfully synthesized by using the intramolecular Diels-Alder reaction. The siloxy- rather than acyloxy-substituents increased the ratio of the endo-cylcoadducts 10 and 12. The oxygen substitution of 9 influenced conformation of the transition state, which was stereochemically restricted by the butenolide moiety. In addition, 9b carrying a hydroxyl group also produced 10b in a similar ratio to 9a. Compound 11 was the only exo-adduct produced in all of the entries.     

Diastereoselective Prins-type reaction of cycloalkenylcyclopropanol silyl ethers and alpha,beta-unsaturated aldehyde acetals

Electrophilic addition of 1-(1-cyclohexenyl)-1-cyclopropanol trimethylsilyl ether to alpha,beta-unsaturated aldehyde acetals under Lewis acidic conditions proceeds with good to excellent diastereoselectivity to afford spirocyclobutanones containing three contiguous stereocenters. A convenient entry to enantioselective syntheses is available by use of a nonracemic C2-symmetric acetal. Elaboration of the resulting adducts provides ready access to medium-sized carbocycles.     

Diastereoselectivity in the directed aldol reactions of 1-fluoro-3,3-dimethyl-butanone enolates and enol silyl ethers.

High diastereoselectivity was observed in the directed aldol reaction of lithium enolates of 1-fluoro-3,3-dimethylbutanone while an apparent reversal of diastereoselection was found in Lewis acid mediated reactions of corresponding enol silyl ethers.     

Photochemical reactions. 140th Communication. Acid-catalyzed rearrangement and electron transfer photooxygenation of cyclopropanols and their silyl ethers

On acid-catalyzed hydrolysis, the tricyclic compounds 2 and 10 , incorporating cyclopropyl-silyl-ether moieties undergo rearrangement to the cis-decalones 3 and 7 , respectively. Hydrolysis of 2 and 10 in the presence of oxygen leads additionally to the formation of the 1,2-dioxolan-3-ols 9 and 13 , respectively, which involves an electron-transfer oxygenation process as could be demonstrated by photooxygenation of the silyl ether 10 and the cyclopropanol 14 in the presence of 9,10-dicyanoanthracene. The configurations of 3 and 9 were assigned by X-ray analysis of the latter compound as well as of the p-nitrobenzoate 8 of 3 .     

Ionic liquids as powerful solvent media for improving catalytic performance of silyl borate catalyst to promote Diels-Alder reactions

Use of the acidic chloroaluminate ionic liquid, including the recycled ones, can improve the catalytic activity of the toluene-coordinated silyl borate in enhancing rates, stereoselectivities, and yields of Diels-Alder reactions.     

Si-H activation of hydrosilanes leading to hydrido silyl and bis(silyl) nickel complexes

A general route for the synthesis of novel NHC stabilized nickel bis(silyl) and nickel hydrido silyl complexes is presented. The reaction of [Ni(2)((i)Pr(2)Im)(4)(COD)] 1 ((i)Pr(2)Im = 1,3-di-isopropyl-imidazolin-2-ylidene) with hydrosilanes H(n)SiR(4-n) leads to complexes of the type [Ni((i)Pr(2)Im)(2)(SiH(n-1)R(4-n))(H)] or [Ni((i)Pr(2)Im)(2)(SiH(n-1)R(4-n))(2)].     

A facile entree to α-oxo sulfines by reaction of thionyl chloride with silyl enol ethers

Silyl enol ethers derived from 1-indanone, 2-indanone, α-tetralone and 4-chromanone react with thionyl chloride to give α-oxo sulfines (3) which can be either isolated or trapped by a cycloaddition reaction with a diene.     

Preparation of siloxacyclopentene containing 1,3-dienes and their Diels-Alder reactions

A number of enynyloxy dimethyl and diisopropyl silanes have been prepared and converted into siloxacyclopentene containing 1,3-dienes via intramolecular hydrosilylation of the alkyne functional group. Diels-Alder reactions of these dienes are reported.