tion of 1,3-diketones and methyl acetoacetate gave exo-methylenecyclopentanes in moderate to good yields with high isomer selectivity. The double allylation step effectively proceeded in the presence of a Ru(II) precatalyst, [Cp*RuCl(cod)], in 1,2-dichloroethane at 90 degrees C. The subsequent cycloisomerization was carried out upon addition of triethylsilane as a hydride source without purification
A combination of a catalytic amount of a Niâphosphine complex and triethylaluminium or chlorodiethylaluminium is able to selectively cyclize a number of 1,7-heptadienes to methylidene(methyl)cyclopentanes and cyclopentenes even in cases where the dienes are prone to deallylation.
Cycloisomerization Promoted by the Combination of a Ruthenium–Carbene Catalyst and Trimethylsilyl Vinyl Ether, and its Application in The Synthesis of Heterocyclic Compounds: 3-Methylene-2,3-dihydroindoles and 3-Methylene-2,3-dihydrobenzofurans
Ruthenium(II)-Catalyzed Isomer-Selective Cyclization of 1,6-Dienes Leading to <i>e</i><i>xo</i>-Methylenecyclopentanes: Unprecedented Cycloisomerization Mechanism Involving Ruthenacyclopentane(hydrido) Intermediate
In the presence of a catalytic amount of ruthenium(II) complexes, [RuCl2(cod)](n), RuCl2(cod)(MeCN)(2), [RuCl2(nbd)](n). [RuCl2(CO)(3)](2), and Cp*Ru(cod)Cl, 1,6-dienes were effectively converted into the corresponding exo-methylenecyclopentanes in good to excellent yields with good isomer purity in i-PrOH at 90 degreesC. The alcoholic solvent was essential for the present catalytic cyclization, and the efficiency increased in the following order: t-BuOH << EtOH less than or equal to i-PrOH. In contrast, a Ru(0) complex. (C6Me6)Ru(cod), catalyzed the cycloisomerization only in 1,2-dichloroethane. The unusual isomer-selectivity occurred when a 1,7-octadiene was subjected to cyclization to give a similar exo-methylenecyclopentane isomer as the major product. The identical isomer selectivity was observed for the cyclization of unsymmetrical 1,6-dienes having one terminal- and one internal-alkene termini. On the basis of the results from the studies using the known ruthenium hydrides and deuterium-labeling substrates, the novel mechanism via the Ru(II) <--> Ru(IV) system involving a ruthenacyclopentane(hydrido) intermediate was proposed, which better explains the particular regiochemistry of the present cyclization than other previous mechanisms.
Grigg, Ronald; Malone, John F.; Mitchell, Thomas R. B., Journal of the Chemical Society. Perkin transactions I, 1984, # 8, p. 1745 - 1754
作者:Grigg, Ronald、Malone, John F.、Mitchell, Thomas R. B.、Ramasubbu, Asnok、Scott, Ronald M.