Balasubrahmanyam, SN and Jayaraj, K (2003) Syn-axial steric and counter-ion coordination factors in the methylation of 6-membered cyclic esters. In: Indian Journal Of Chemistry Section B-Organic Chemistry Including Medicinal Chemistry, 42 (5). pp. 1098-1110.
syn_axial.pdf - Accepted Version
It was found in an earlier study that one (A) of the four possible configurational isomers of trimethyl 1-methylcyclohexane-1,2,3-tricarboxylate yields, in regiospecific and highly stereospecific manner, trimethyl trans, meso 1,2-dimethylcyclohexane-1,2,3-tricarboxylate on exposure to the methylation condition of treatment with tritylsodium (ether)/methyl iodide. Isomer A changes to isomer C via enolate formation unexpectedly slowly even though what was needed for the transformation was only a ring inversion. Equally unexpectedly, it was found in an independent experiment that an alpha-enolate is not formed at all directly from C on treatment with tritylsodium. The role that coordination of counterion (Na+) may play in the first case and manner in which 1,3-syn axial steric effect may operate in the second was sought to be tested by employing methyl 9-ethoxycarbonyl- and methyl 9-methyl trans-decalin-2-carboxylates as test systems having no possibility of ring-inversion. The 9-methyl system, analogue of C, did not form an alpha-enolate ion, as expected. On the other hand, the 9-ester, analogue of A, readily formed an enolate that does not undergo methylation under conditions when A does. It did undergo the reaction, practically non-stereoselectively however, when the strong de-coordinating agent hexamethyl phosphoric triamide was added before the addition of methyl iodide.
|Item Type:||Journal Article|
|Additional Information:||Copyright of this article belongs to National Institute of Science Communication.|
|Department/Centre:||Division of Chemical Sciences > Organic Chemistry|
|Date Deposited:||26 Nov 2009 08:24|
|Last Modified:||30 Mar 2012 10:13|
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