Michio Obayashi

(Diethylphosphinyl)difluoromethyllithium. — Preparation and synthetic application —

Abstract The action of lithium diisopropylamide on diethyl difluoromethylphosphonate gives the title reagent which reacts with various electrophiles to introduce difluoromethylene or difluoromethyl unit.

Cyanotrimethylsilane as a versatile reagent for introducing cyanide functionality

Abstract Cyanotrimethylsilane adds to some ⇌,β-unsaturated ketones in conjugate manner under the catalytic action of Lewis acids such as triethylaluminium, aluminium chloride, and SnCl 2 . Hydrolysis of the products gives β-cyano ketones which are identical to the hydrocyanated products of the starting enones. The title silicon reagent reacts with acetals and orthoesters under the catalytic action of SnCI 2 or BF 3 -OEt 2 affording 2-alkoxy- and 2,2-dialkoxyalkanenitriles. Application of the reaction to O-protected β- D -ribofuranoses gives selectively β-d-ribofuranosyl cyanide in excellent yield.

Fluoride ion-catalyzed generation and carbonyl addition of α-halo carbanions derived from α-halo organosilicon compounds

Abstract The title carbanion species are generated from the corresponding α-haloorganosilicon compounds by the action of a catalytic amount of tris(diethylamino)sulfonium difluorotrimethylsilicate and are found to undergo addition to aldehyde carbonyl efficiently at ambient temperature. The synthetic potential of the reaction is demonstrated by application to the synthesis of some insecticides.

Preparation and carbonyl addition of γ,γ-difluoroallylsilanes

Abstract The reaction of 3,3,3-trifluoropropenes with disilane/tetrabutylammonium fluoride or silyllithium reagent gives γ,γ-difluoroallylsilanes which afford gem-difluoroallyl adducts of aldehydes and ketones with the aid of a catalyst such as potassium t-butoxide o r tris(diethylamino)sulfonium difluorotrimethylsilicate.

Conjugated addition of cyanotrimethylsilane to α,β-unsaturated ketones

Abstract Triethylaluminium-mediated reaction of cyanotrimethylsilane with 6-methylbicyclo[4.4.0]dec-1-en-3-one affords a mixture of diastereomeric 1,4-adducts. The reaction is kinetically controlled in toluene, whereas thermodynamically in refluxing THF. 4-Methyl-3-penten-2-one and carvone analogously give the respective 1,4-adducts and a conjugated dienone addords the 1,6-adduct in good yield.

An improved procedure for the synthesis of 1,1-difluoro-2-hydroxyalkylphosphonates

Abstract The reaction of diethyl difluoro(trimethylsilyl)methylphosphonate with arenecarbaldehydes and aryl methyl ketones is effected with the aid of a catalyst. cesium fluoride, at room temperature to afford the title compounds.

A regio- and stereoselective synthesis of 1,2-disubstituted vinylsilanes

Abstract The alkylcopper reagents prepared from RMgBr and CuBr react with trimethylsilylacetylene to give regio- and stereo-selectivity 1-trimethylsilyl-1(Z)-alkenylcopper adducts. Hydrolysis affords 1-trimethylsilyl-1(E)-alkenes exclusively. Alkylation, acylation, halogenation, and stannylation proceed stereoselectively to afford synthetically useful intermediates. Homopropargylation of alkyl 1-trimethylsilyl-1(Z)-alkenylcuprates provided better yield than that of the original vinylcopper reagents.

Reaction of trialkylboranes with 2-bromo-6-lithiopyridine: Stereospecific alkylative cleavage of pyridine ring

Abstract Reaction of 2-bromo-6-lithiopyridine with trialkylboranes affords 5-alkyl-5-dialkylboryl-2-( Z ), 4( E )- pentadienenitriles by stereospecific alkylative cleavage of the pyridine ring. These intermediary vinylboranes are versatile reagents for the preparation of 5-alkyl-2( Z ), 4( E )-pentadienenitriles, 5,5-dialkyl-4-pentenenitriles and 5,5-dialkyl-2,4-pentadienenitriles.

Epoxidation of allyl and homoallyl trimethylsilyl ethers with t-butyldioxytrimethylsilane and silicon lewis acid/vanadium catalyst

Abstract Trimethylsilyl ethers of allyl and homoallyl alcohols are epoxidized with t-butyldoxytrimethylsilane and a catalyst system consisting of vanadyl acetoacetate and tris(trimethylsilyl)phosphate. Stereoselectivities of the oxidation are compared with the epoxidation of allyl alcohols with t-BuOOH/V catalyst and with m-chloroperbenzoic acid.

Insertion of alkanal carbonyl and 1,3-diene units between SiSi bonds of trisilanes. Synthesis of novel silicon-containing materials

Abstract Octamethyltrisilane/tetrabutylammonium fluoride reagent allows us to insert A=B (e.g. alkanals and 1,3-dienes) between the SiSi bonds to produce Si-A-B-Si-B-A-Si structure in one step or Si-A-B-Si-B′-A′-Si step by step.