Mg‐Promoted Selective C—F Bond Cleavage: A General and Efficient Access to Difluoroenol Silyl Ethers and Their Derivatives

Abstract

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C−F Bond Activation in Organic Synthesis

“…In the previous section, the electrochemical methods have hitherto been developed for reductive defluorination of a trifluoromethyl group, and they can be successfully applied to the preparation of difluoromethylene building blocks. In 1999, Amii and Uneyama reported that metallic magnesium, which serves as a more convenient electron source, proves useful for the C−F bond breaking process of trifluoromethyl ketones 677 to provide a practical route to 2,2-difluoroenol silyl ethers 682 (Scheme ). ,, …”

“…C−F bond activation triggered by Brook rearrangement is applicable to the preparation of 2,2-difluoroenol silyl ethers . α-Silyl-α-trifluoromethylalkoxylates 974 are generated in situ by one of the three possible reactions: reaction of acyl silanes 972 with CF 3 SiMe 3 , trifluoroacetyl silanes 973 with alkyl lithiums, and trifluoromethyl ketones 677 with trialkylsilyl anions, respectively (Scheme ).…”

“…The higher reactivity of fluorine than those of chlorine and bromine is demonstrated by the reactions of 1-bromo-3-chloro-5-fluorobenzene (237) with carbon 110 and oxygen 111 nucleophiles, where only 2% of 3-chloro-5-fluorobenzene is obtained in the reaction of 237 with cyanoacetate (Scheme 76). Upon treatment with 1 equiv of i-PrSNa, 3-fluorobromobenzene ( 240) is converted to 3-bromo-( 241) and 3-fluorophenyl isopropyl sulfide (242) in the ratio 70:3. 112 A big reactivity difference is also shown in the reaction of 243 with phosphorus 113 and nitrogen 114…”

Preparation of 1-aryl-2,2-difluoro enol esters via dehydrosulfonylation of α-(phenylsulfonyl)difluoromethylated benzoates

“…Trifluoroethanol has been widely used as an inexpensive starting material for prepation of 2,2-difluoro enol derivatives [4]. More recently, a novel C-F bond cleavage chemistry with trifluoromethyl compounds has been developed by Uneyama and co-workers, which significantly expanded both the preparation and the synthetic applications of 2,2-difluoro enol building blocks [5,9]. However, compared to the 2,2-difluoro enol silyl ethers, 2,2-difluoro enol carboxylic esters are less explored [6,8].…”

“…2,2-Difluoro enol derivatives (such as 2,2-difluoro enol silyl ethers) are important fluorine-containing building blocks for the synthesis of many gem-difluorinated organic compounds [1][2][3][4][5]. Initially, 2,2-difluoro enol silyl ethers were prepared from chlorodifluoromethyl ketones [6] or from acyltrifluoromethylsilane through Brook rearrangement [7,8].…”