ChemInform Abstract: A Novel and Highly Efficient Synthesis of gem‐Difluorocyclopropanes.

Abstract

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Pd‐Catalyzed Transfer of Difluorocarbene for Three Component Cross‐Coupling†

“…[ 1 ] Difluorocarbene has proved to be a valuable intermediate for fluorine incorporation. [ 2 ] Typical difluorocarbene reactions include [2+1] cyclization of alkenes/ alkynes [ 3 ] and difluoromethylation of X—H bonds (X = heteroatom). [ 4 ] Hu disclosed an efficient C—H difluoromethylation by using TMSCF 2 Br, a reagent developed by them recently, [ 5 ] as a difluorocarbene source.…”

Synthesis of Alkylidene(gem-Difluorocyclopropanes) from Propargyl Glycolates by a One-Pot Difluorocyclopropenation/Ireland–Claisen Rearrangement Sequence

“…The difluorocyclopropenation of the triple bond in 3a was initially attempted using Ruppert-Prakash's reagent (TMSCF 3 , 2 equiv) in the presence of NaI (2.2 equiv) in THF (sealed tube, 80 °C, 2 h) 17 but the 3,3-difluorocyclopropene 4a was isolated in modest yield (43%) because unidentified side-products were formed. Much more satisfactory results were obtained by slow addition (via syringe pump within 2 h) of an excess of Dolbier's reagent (trimethylsilyl fluorosulfonyldifluoroacetate, TFDA) 18 to a concentrated solution (c = 2 M) of propargyl glycolate 3a in diglyme at 120 °C. The desired 3,3difluorocyclopropene 4a was isolated in 86% yield after purification by flash column chromatography on silica gel.…”