The efficient copper-catalyzed addition reaction of bis(pinacolato)diboron to alpha,beta-acetylenic esters has been developed, which produces the corresponding beta-borylated-alpha,beta-ethylenic esters in high yields under mild reaction conditions.
A synthesis of natural tetrahydrofuran lignan (+)-sylvone is achieved starting from methyl allenoate in 5 steps. The synthesis begins from an enantioselective aldol reaction of methyl allenoate with 3,4-dimethoxybenzaldehyde to afford α-addition aldol adduct. Key steps for the synthesis of sylvone include an oxacyclization of the α-hydroxy allenyl adduct followed by a Michael addition of a 1,3-dithiane derivative to establish a sylvone skeleton with suitable stereoselections.
The effect of heat and ultraviolet irradiation on dimethyltin dihydride is reported. At 120°, the major decomposition products are (CH3)3SnH, Sn, and Hz, with a small amount of (CH3)6Snz.At 130" under ultraviolet light, decomposition is much more rapid giving (CH3)3SnH, Sn, and Hz, and an appreciable quantity of (CH3)rSn. If the dihydride is maintained under these conditions for a longer period (40 hours), (CH3)6Sn? is formed in place of (CH8)3SnH, and other products are (CH3)4Sn, Sn, and Hz. Negligible decomposition occurs a t 25' even under irradiation.
The H1 and Fl9 magnetic resonance spectra of three tin compounds have been examined. Taking advantage of C13, Sn117, and Sn119 being magnetic nuclei in sinall natural abundance, it has been possible t o obtain 31 coupling constants from the spectra.
The reactions of methyltin hpdrides with rnethylperfluorovillyltin compounds have been examined under heat or ultraviolet irradiation. In no case is there evidence of addition to the C=C bond. Instead, extensive reduction of the vinyl group occurs to give cis-l,2-difluorovinyltin derivatives as the principal products, with smaller amounts of the trans-1,2-difluorovinyltin isomers, 2,2'-difluorovinyltin compounds, and products containing one or more -CzH?F groups. Trimethyl-or dimethyl-tin fluoride is formed quantitatively from the corresponding hydride. In the reaction of dimethyl bis(perfluorovinyl)tin with dimethyltin dihydride, vinyl-hydrogen exchange occurs a t 60° in the dark to give din~ethylperfluorovinyltin hydride, while under ultraviolet irradiation partially fluorinated vinyltin compou~lds are formed. On the other hand, no reaction takes place between dimethyl bis(perfluoroviny1)tin and 2 moles of trimethyltin hydride in the dark a t 50°, but under ultraviolet irradiation a t 25", partial vinyl-hydrogen exchange occurs, accompanied by reduction, to yield both trimethyl and dimethyl partially fluorinated vinyltin compounds. 'The infrared and proton magnetic resonance spectra of the products are discussed.
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