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-OXIDE AND TRANS-OXIDE OF 4-[(BENZYLOXY)METHYL]CYCLOHEXENE, 3-CYCLOHEXENEMETHANOL, AND METHYL 3-CYCLOHEXENECARBOXYLATE
CROTTI, PAOLO;PINESCHI, MAURO
1992-01-01
Abstract
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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
