Polyhalogenation-Facilitated Spirolactonization at the meta-Position of Phenols
Jiaqi Cao1, Youcai Ma1, Liangzhen Hu1
1School of Chemistry and Chemical Engineering, and Chongqing Key Laboratory of Theoretical and Computational Chemistry, Chongqing University, Chongqing 401331, China.
Abstract:
A novel dearomative spirolactonization/polyhalogenation of phenols that employs hypervalent iodine PhICl2 (iodobenzene dichloride) as both an oxidant and chlorine source with an indispensable base, or only using NBS (N-bromosuccinimide) without any additives, is presented. Halide participations are a vital factor in the cascade reaction of 3'-hydroxy-[1,1'-biphenyl]-2-carboxylic acids with good selectivities and reactivities and induced the rapid constructions of multiple C-halogen bonds and directional C═O bonds in a one-step operation under mild conditions. In gaining a good understanding of the mechanism, the increase in number of bromine atoms was inferred rationally from the spirolactonization process, assisted by DFT calculations and high-resolution mass spectrometry. Mechanistic experiments suggest that the formation of a stable carbocation intermediate plays a great role in the migration of oxygen to spirolactonization.
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