Reactions of Fischer Carbene Complexes with Siloxydienes: Formation of Cycloheptadiene and Cyclopentene Derivatives—Formal [2+1] Cycloaddition Followed by Cope Rearrangement Versus Formal [3+2] Cycloaddition with or without Preceding Carbene-Ligand Metathesis
摘要:
Thermal reactions of the alpha,beta-unsaturated Fischer carbene complexes 3-5 with the siloxydienes 6 and 7 mainly furnished the expected cyclohepta-1,4-dienes such as 9, 10, 12, 14, and 15, whose formation is explained by a formal [2+1] cycloaddition followed by Cope rearrangement. The rather electron-rich carbene complex 5 also afforded the cyclopentene derivatives II and 16 as by-products, which are probably formed by two distinct mechanisms. Single diastereomers of the cyclopentene derivatives 17 and 18 were isolated as the exclusive products of the reactions of 3 and 4, respectively, with the donor/acceptor-substituted 1,3-diene 8. This process is interpreted as a metalla Diels-Alder reaction to form a chromacyclohexene intermediate 25, which subsequently undergoes fragmentation to give cyclopentene derivatives with the required constitution. Most surprisingly, the reactions of simple carbene complexes 1 or 2 with the siloxydienes 7 or 8 yielded cyclopentene derivatives 19 and 20 that do not contain the carbene ligand of the precursor complexes. Instead, the constitution of the isolated products can be accounted for by a formal diene dimerization with fragmentation of a methylene unit. Their formation can be interpreted by an unprecedented sequence of carbene-ligand metathesis followed by a metalla Diels-Alder reaction and reductive fragmentation. All these results illustrate the great importance of electronic fine-tuning in the precursors involved in reactions of Fischer carbene complexes with 1,S-dienes.
The nucleophilic cyclopropanation of hexa-1,5-diene-3,4-diones with bis(iodozincio)methane afforded the Zn alkoxides of cis-dialkenylcyclopropane-1,2-diols stereoselectively. The subsequent oxy-Cope rearrangement afforded the corresponding Zn alkoxides of 5,6-dialkylcyclohepta-3,7-diene-1,3-diols.
Treatment of 1,6-dialkylhexa-1,5-diene-3,4-diones with bis(iodozincio)methane gave zinc alkoxides of cis-5,6-dialkylcyclohepta-3,7-diene-1,3-diol in good yields at room temperature. The reaction proceeded with high stereospecificity. Bis(iodozincio)methane converted the diketone into the cis-divinylcyclopropane-1,2-diol stereoselectively; this diol transformed into the corresponding cycloheptane derivative
Treatment of 1,6-dialkylhexa-1,5-diene-3,4-diones with bis(iodozincio)methane at −78 °C for several hours gave cis-dialkenylcyclopropane-1,2-diols which rearranged into the zinc alkoxides of cis-5,...
1,6-二烷基六-1,5-二烯-3,4-二酮在 -78 °C 下用双(碘锌)甲烷处理数小时,得到顺式二烯基环丙烷-1,2-二醇,其重排为顺式5,...
Reactions of Fischer Carbene Complexes with Siloxydienes: Formation of Cycloheptadiene and Cyclopentene Derivatives—Formal [2+1] Cycloaddition Followed by Cope Rearrangement Versus Formal [3+2] Cycloaddition with or without Preceding Carbene-Ligand Metathesis
Thermal reactions of the alpha,beta-unsaturated Fischer carbene complexes 3-5 with the siloxydienes 6 and 7 mainly furnished the expected cyclohepta-1,4-dienes such as 9, 10, 12, 14, and 15, whose formation is explained by a formal [2+1] cycloaddition followed by Cope rearrangement. The rather electron-rich carbene complex 5 also afforded the cyclopentene derivatives II and 16 as by-products, which are probably formed by two distinct mechanisms. Single diastereomers of the cyclopentene derivatives 17 and 18 were isolated as the exclusive products of the reactions of 3 and 4, respectively, with the donor/acceptor-substituted 1,3-diene 8. This process is interpreted as a metalla Diels-Alder reaction to form a chromacyclohexene intermediate 25, which subsequently undergoes fragmentation to give cyclopentene derivatives with the required constitution. Most surprisingly, the reactions of simple carbene complexes 1 or 2 with the siloxydienes 7 or 8 yielded cyclopentene derivatives 19 and 20 that do not contain the carbene ligand of the precursor complexes. Instead, the constitution of the isolated products can be accounted for by a formal diene dimerization with fragmentation of a methylene unit. Their formation can be interpreted by an unprecedented sequence of carbene-ligand metathesis followed by a metalla Diels-Alder reaction and reductive fragmentation. All these results illustrate the great importance of electronic fine-tuning in the precursors involved in reactions of Fischer carbene complexes with 1,S-dienes.