Vitamin B12-Catalyzed Dicarbofunctionalization of Bromoalkenes Under Visible Light Irradiation

Abstract

Vitamin B12 plays a crucial role in enzymatic transformations. This natural compound proved also useful as a catalyst in numerous organic reactions. Commercial availability and lower cost than precious metal complexes, make cobalamin an attractive candidate for a broader use as a benign Co-catalyst. Herein, the vitamin B12-catalyzed dicarbofuntionalization of bromoalkenes with electrophilic olefins is reported leading to substituted pyrrolidines and piperidines in decent yields after only 15 minutes under light irradiation.

C–C Bond Forming Reactions Enabled by Vitamin B12─Opportunities and Challenges

“…The reaction proceeds via a sequence of debromination, radical cyclization with the formation of an N-heterocycle, followed by conjugate addition (Scheme 6). 23 This protocol enables the efficient synthesis of substituted heterocycles 19 in as fast as 15 min and is also compatible with internal alkenes and alkynes, correspondingly leading to bicyclic product 19b or the derivative with the exocyclic double bond 19d.…”

Vinyl Azides as Radical Acceptors in the Vitamin B12-Catalyzed Synthesis of Unsymmetrical Ketones

“…These, at higher temperatures or higher levels of light irradiation, are prone to homolytic cleavage generating radicals. Thus, vitamin B 12 catalysis enables formation of radicals from various electrophilic precursors; these include organic halides, , epoxides, diazo compounds, and strained molecules …”

Bioinspired Photocatalyzed Organic Synthetic Transformations. The Use of Natural Pigments and Vitamins in Photocatalysis

“…Gryko and collaborators [104] reported a native vitamin B 12 (cyanocobalamin)‐catalyzed intramolecular cyclization of bromoalkenes for the synthesis of pyrrolidines and piperidines (Scheme 28, equation A), whereas upon addition of an electron deficient olefin to the reaction media dicarbofunctionalization takes place (Scheme 28, equation B). Both reactions employ native vitamin B 12 as catalyst, Zn/NH 4 Cl as reducing agent, in methanol as solvent under visible light irradiation; the reaction without the addition of the electrophilic olefin proceeds under visible light irradiation as opposed to the dicarbofunctionalization where blue LEDs are necessary for maximizing the reaction yield.…”

“…Regarding some mechanistic aspects, [104] the reaction is initiated by reduction of Co(III) in B 12 to Co(I) promoted by Zn/NH 4 Cl. The supernucleophilic Co(I) form of B 12 reacts with the bromoalkene affording an alkylcobalamin I (Scheme 29) and bromide anion.…”