Ionic iodocarbocyclization reactions of 4-alkenyl- and 4-alkynylmalonate derivatives
摘要:
The cyclization reactions of dimethyl 4-alkenylmalonate derivatives la-d in the presence Of 12 and Ti(Ot-Bu)4 proceed in a highly regio- and stereocontrolled manner (5-exo cyclization and trans addition) to give (iodoalkyl)cyclopentane derivatives 2 or bicyclic lactones 3 through the displacement of the iodide of 2 by an ester group. Iodocarbocyclization reactions of dimethyl [(cycloalkenyl)alkyl]malonates 1g-i or dimethyl [(methylenecycloalkyl)alkyl]malonates 1j and 1k proceed regio- and stereoselectively to give fused ring compounds or spiro compounds, respectively, as single isomers. Similar reactions of 4-alkynyl derivatives 5 give preferentially E-iodomethylene cyclopentane derivatives 6. An ionic mechanism rather than a radical mechanism is suggested on the basis of the regioselectivity and stereospecificity of the above reactions.
A new entry to carbocycles: synthesis of cyclopentene and cyclohexene derivatives through endo-mode ring closure of allenyl sulfones
作者:Chisato Mukai、Rie Ukon、Norikazu Kuroda
DOI:10.1016/s0040-4039(03)00067-4
日期:2003.2
Treatment of dimethyl 4-(phenylsulfonyl)-4,5-hexadiene-1,1-dicarboxylate with potassium tert-butoxide in tert-butanol at room temperature effected successive endo-mode ring closure at the sp-hybridized carbon center and demethoxycarbonylation of the resulting malonate derivative leading to the exclusive formation of methyl 2-methyl-3-(phenylsulfonyl)-1-cyclopentenecarboxylate. An additional seven allenyl