Activation of 1,1-Difluoro-1-alkenes with a Transition-Metal Complex:  Palladium(II)-Catalyzed Friedel–Crafts-Type Cyclization of 4,4-(Difluorohomoallyl)arenes

Abstract

Cationic palladium(II) ([Pd(MeCN)4](BF4)2) provides the first transition-metal-catalyzed method for electrophilic activation of electron-deficient 1,1-difluoro-1-alkenes, which allows their Friedel-Crafts-type cyclization with an intramolecular aryl group via a Wacker-type process. By using BF3.OEt2, the cyclization was effected by a catalytic amount of the palladium without its reoxidation.

A facile and efficient synthesis of 2-amino-3-cyano-4H-chromenes and tetrahydrobenzo[b]pyrans using 2,2,2-trifluoroethanol as a metal-free and reusable medium

“…Therefore, the search continues for a better catalyst for the synthesis of pyrans in terms of operational simplicity, reusability, economic viability, and greater selectivity. The use of fluorinated solvent, as chemical reaction media in place of conventional volatile organic solvents, has grown dramatically in recent years [35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50]. Fluorinated alcohols possess interesting physiochemical properties, which include lower boiling points and higher melting points than their non-fluorinated counterparts, high polarity, strong hydrogen bond donation properties and the ability to solvate water.…”

Palladium-Mediated Organofluorine Chemistry

“…In fact, the experimental examples where β-F elimination are reported occur on derivatives where β-H elimination is not possible. [248][249][250][251] The reactivity of σ-perfluoroalkyl metal complexes is largely dominated by α-fluorine elimination processes, which lead to the formation of fluorocarbene derivatives (Scheme 105). …”

A Novel One-Pot Synthesis of Quinoxaline Derivatives in Fluorinated Alcohols

“…34 The main advantage of fluorinated alcohols, for example hexafluoroisopropanol (HFIP) and trifluoroethanol (TFE), is the possibility to carry out, in the absence of promoting agents, reactions that usually require the aid of Lewis acids or catalysts. [35][36][37][38][39][40][41][42][43][44][45][46][47][48][49] In addition, they can be easily separated from the reaction mixture for subsequent reuse. Due to the current challenges for developing environmentally benign synthetic processes and in continuation of our interest in the application of fluorinated solvents for various organic transformations [50][51][52][53][54][55][56] we report a new, convenient, mild and efficient procedure for the synthesis of quinoxaline derivatives by the reaction of aryl 1,2-diamines with 1,2-dicarbonyl compounds under mild reaction conditions in hexafluoroisopropanol (HFIP) (Scheme 1).…”