[reaction: see text] The rhodium(I)-catalyzed methylenation of ketones using trimethylsilyldiazomethane proceeds to give the corresponding alkenes in good yields (60-97%). The use of an excess of 2-propanol and 1,4-dioxane as a solvent were instrumental to obtain the desired alkenes in high yields. Superior results were achieved with the rhodium(I)-catalyzed methylenation in comparison with the standard
Terminal alkenes have been efficiently prepared via a rhodium-catalyzed olefination procedure using Wilkinson’s catalyst in the presence of triphenylphosphine, 2-propanol and trimethylsilyldiazomethane. Optimized reaction conditions are described for aldehydes and ketones, as well as alternative work up procedures.
Transmetalation reactions of organosamarium reagents. Chlorosilane-accelerated copper-catalyzed conjugate additions
作者:Peter Wipf、Srikanth Venkatraman
DOI:10.1021/jo00064a040
日期:1993.6
TMSCl accelerates the conjugate addition of in situ prepared organosamarium reagents to alpha,beta-unsaturated carbonyl compounds and nitriles in the presence of HMPA and catalytic amounts of Cu(I) salts. Reactions at -78-degrees-C leads to silyl enol ethers which are isolated or cleaved with TBAF to give beta-alkylated ketones in 30-90% overall yield. Catalysis is most efficient in the presence of 4 equiv of TMSCl and HMPA. HMPA is also necessary for the in situ preparation of the organosamarium species from alkyl halide and SmI2. Some functional groups (chloride,ether,alkene, amide) are tolerated in this process. In the absence of Cu(I) salts, 1,2-additions of organosamarium reagents to carbonyl groups are also dramatically accelerated by TMSCl/HMPA and occur within minutes at -78-degrees-C.
Conjugate addition reactions of organosamarium species via in situ transmetalation to copper(I) salts
作者:Michael J. Totleben、Dennis P. Curran、Peter Wipf
DOI:10.1021/jo00032a027
日期:1992.3
Preformed organosamarium species, available by reduction of aryl or alkyl halides with SmI2, were treated with copper(I) salts to effect in situ transmetalation and conjugate addition to enones. In a series of copper(I) salts, CuI.P(OEt)3 gave best results in combination with 2 equiv of organosamarium reagent. This new method allows the multiple formation of carbon-carbon bonds through a combination of radical and cuprate chemistry.