Mechanistic Studies of Vitamin B(12)-Catalyzed Dechlorination and Carbon-Carbon Bond-Forming Reactions

In the presence of catalytic vitamin B12 and a reducing agent such as TI(III)citrate or Zn, arylalkenes can be dimerized with unusual regioselectivity forming a new carbon-carbon bond between the benzylic carbons of each coupling partner. Dimerization products were obtained in good to excellent yields for mono- and 1,1-disubstituted alkenes, and dienes containing one aryl alkene underwent intramolecular cyclization in good yields. 1,2-Disubstituted and trisubstituted alkenes were unreactive. Mechanistic investigations using radical traps suggest the involvement of benzylic radicals, and the lack of diastereoselectivity in the product distribution is consistent with dimerization of two such reactive intermediates. A strong reducing agent is required for the reaction and fulfills two roles. It returns the Co(II) form of the catalyst generated after the reaction to the active Co(I) state, and by removing Co(II) it also prevents the non-productive recombination of alkyl radicals with cob(II)alamin. The mechanism of the formation of benzylic radicals from arylalkenes and cob(I)alamin poses an interesting problem. The results with a one-electron transfer (et) probe indicate that the radical generation is not likely to involve an electron transfer. Several alternative mechanisms are discussed.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Chemistry

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2015

Author dc:creator

• Shey, Justin

Contributors dc:contributor

• van der Donk, Wilfred A.

• Chemistry, Organic

Language dc:language

eng

Identifier

(MiAaPQ)AAI3070434

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/84090