Cobalamins elimination reactions

Cobalamin catalysed electrochemical reduction of the 2-chloroethanol ester 68 at negative potentials, without photochemical assistance, leads to a 1,2-elimination process (see p. 115) [228]. This contrasts with the lack of 1,2-elimination during reaction of 66 and 67, Thus in the purely electrochemical carbon-cobalt bond... 

By pairing an addition to an enone in the final step with an initial intramolecular radical cyclization, it is possible to accomplish tandem radical reactions of cobalamine(III) alkyls356. Tandem cyclizations are also most often done, with the final termination step being elimination to the alkene or trapping with styrene (equation 182)357. It is also possible to enter into ring-expansion reactions by retrograde radical cyclization-recyclization processes in modest yields358. 

Irradiation of trans-[P(C2H5)3]2PtClH and CF3— C=CH produced cis-[P(C2H5)3]2PtCl-C(CF3)=CHa 213b Elimination of C2H4 from —Co—C2H5 in ethyl-cobalamine and the (intermediate) formation of —Co—H can be looked upon as the reversal of this type of reaction 402>. 

The decomposition of alkylcobalamin by j8-elimination of H, whether by a route analogous to (18) or (20), is impossible in neopentyl and benzyl cobalamins and cobinamides. Schrauzer s group has studied the decomposition, in the absence and presence of O2, of such compounds. The slowness of the reaction under the first conditions points to reactions (14) and (26), equilibrium lying to the left in the former and the latter... 

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