Regiochemical control of the ring-opening of 1,2-epoxides by means of chelating processes. 2. Synthesis and reactions of the cis- and trans-oxides of 4-[(benzyloxy)methyl]cyclohexene, 3-cyclohexenemethanol, and methyl 3-cyclohexenecarboxylate
摘要:
The synthesis of the diastereoisomeric epoxides cis-1b-d and trans-2b-d and the products of their ring-opening by various nucleophiles are described. The results of the ring-openings of the trans-epoxides 2b-d can be rationalized by combining stereoelectronic and conformational arguments. However, the regioselectivity of the ring-openings of the cis-epoxides 1b-d can, in principle, be influenced by the chelation of a metal ion by the oxygen atom of the epoxy group and that of the substituent on the 4-position. The results of the reactions of the cis-epoxides 1b-d indicate that, to some degree, chelation is indeed a factor. How important a factor it is is dependent both on the reaction conditions and on the concentration and nature of the metal ion. In the ring-openings of the cis-epoxides 1b and 1d, chelation seems to be a larger factor than it is in the ring-openings of cis-epoxide 1c. However, in no case is chelation as large a factor as it was in the ring-openings of the cis-epoxide 1a, which was studied earlier. On the other hand, the autocatalyzed methanolysis, under neutral conditions, of epoxy acid 1e, followed by CH2N2 methylation of the crude product, afforded a mixture of the two regioisomeric hydroxy ethers in which the C-2-type compound predominates. This result suggests that intramolecular hydrogen bonding may determine the reactive conformation of 1e.
Regiochemical control of the ring-opening of 1,2-epoxides by means of chelating processes. 2. Synthesis and reactions of the cis- and trans-oxides of 4-[(benzyloxy)methyl]cyclohexene, 3-cyclohexenemethanol, and methyl 3-cyclohexenecarboxylate
摘要:
The synthesis of the diastereoisomeric epoxides cis-1b-d and trans-2b-d and the products of their ring-opening by various nucleophiles are described. The results of the ring-openings of the trans-epoxides 2b-d can be rationalized by combining stereoelectronic and conformational arguments. However, the regioselectivity of the ring-openings of the cis-epoxides 1b-d can, in principle, be influenced by the chelation of a metal ion by the oxygen atom of the epoxy group and that of the substituent on the 4-position. The results of the reactions of the cis-epoxides 1b-d indicate that, to some degree, chelation is indeed a factor. How important a factor it is is dependent both on the reaction conditions and on the concentration and nature of the metal ion. In the ring-openings of the cis-epoxides 1b and 1d, chelation seems to be a larger factor than it is in the ring-openings of cis-epoxide 1c. However, in no case is chelation as large a factor as it was in the ring-openings of the cis-epoxide 1a, which was studied earlier. On the other hand, the autocatalyzed methanolysis, under neutral conditions, of epoxy acid 1e, followed by CH2N2 methylation of the crude product, afforded a mixture of the two regioisomeric hydroxy ethers in which the C-2-type compound predominates. This result suggests that intramolecular hydrogen bonding may determine the reactive conformation of 1e.
40. Aspects of stereochemistry. Part XI. Epoxide formation in the cyclohexene and bicycloheptene series
作者:H. B. Henbest、B. Nicholls
DOI:10.1039/jr9590000221
日期:——
Regiochemical control of the ring-opening of 1,2-epoxides by means of chelating processes. 2. Synthesis and reactions of the cis- and trans-oxides of 4-[(benzyloxy)methyl]cyclohexene, 3-cyclohexenemethanol, and methyl 3-cyclohexenecarboxylate
作者:Marco Chini、Paolo Crotti、Lee A. Flippin、Franco Macchia、Mauro Pineschi
DOI:10.1021/jo00031a018
日期:1992.2
The synthesis of the diastereoisomeric epoxides cis-1b-d and trans-2b-d and the products of their ring-opening by various nucleophiles are described. The results of the ring-openings of the trans-epoxides 2b-d can be rationalized by combining stereoelectronic and conformational arguments. However, the regioselectivity of the ring-openings of the cis-epoxides 1b-d can, in principle, be influenced by the chelation of a metal ion by the oxygen atom of the epoxy group and that of the substituent on the 4-position. The results of the reactions of the cis-epoxides 1b-d indicate that, to some degree, chelation is indeed a factor. How important a factor it is is dependent both on the reaction conditions and on the concentration and nature of the metal ion. In the ring-openings of the cis-epoxides 1b and 1d, chelation seems to be a larger factor than it is in the ring-openings of cis-epoxide 1c. However, in no case is chelation as large a factor as it was in the ring-openings of the cis-epoxide 1a, which was studied earlier. On the other hand, the autocatalyzed methanolysis, under neutral conditions, of epoxy acid 1e, followed by CH2N2 methylation of the crude product, afforded a mixture of the two regioisomeric hydroxy ethers in which the C-2-type compound predominates. This result suggests that intramolecular hydrogen bonding may determine the reactive conformation of 1e.