Aflatoxin B2 Synthesis
The total synthesis of Aflatoxin B2 is a multistep sequence that begins with a cycloaddition between the quinone 1 and the 2,3-Dihydrofuran. This reaction is catalyzed by a CBS catalyst and is enantioselective. The next step is the orthoformylation of reaction product 2 in a Duff reaction. The hydroxyl group in 3 is esterified with triflic anhydride which adds a triflate protecting group. This step enables a Grignard reaction of the aldehyde group in 4 with methylmagnesiumbromide to the alcohol 5 which is then oxidized with the Dess-Martin periodinane to the ketone 6. A Baeyer-Villiger oxidation converts the ketone to an ester (7) and a reduction with Raney nickel converts the ester into an alcohol and removes the triflic acid group. In the final step the coumarin skeleton is added to 9 by a combined coupling reaction with zinc carbonate of the vinyl bromide in 8 and a transesterification step between the phenol group and the ethyl ester group.
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