ABSTRACT
Transition metal catalysis plays a pivotal role in transforming unreactive C-H bonds. However, regioselective activation of distal aliphatic C-H bonds poses a tremendous challenge, particularly in the absence of directing templates. Activation of a methylene C-H bond in the presence of methyl C-H is underexplored. Here we show activation of a methylene C-H bond in the presence of methyl C-H bonds to form unsaturated bicyclic lactones. The protocol allows the reversal of the general selectivity in aliphatic C-H bond activation. Computational studies suggest that reversible C-H activation is followed by ß-hydride elimination to generate the Pd-coordinated cycloalkene that undergoes stereoselective C-O cyclization, and subsequent ß-hydride elimination to provide bicyclic unsaturated lactones. The broad generality of this reaction has been highlighted via dehydrogenative lactonization of mid to macro ring containing acids along with the C-H olefination reaction with olefin and allyl alcohol. The method substantially simplifies the synthesis of important bicyclic lactones that are important features of natural products as well as pharmacoactive molecules.
ABSTRACT
The Fujiwara-Moritani reaction is a powerful tool for the olefination of arenes by Pd-catalysed C-H activation. However, the need for superstoichiometric amounts of toxic chemical oxidants makes the reaction unattractive from an environmental and atom-economical view. Herein, we report the first non-directed and regioselective olefination of simple arenes via an electrooxidative Fujiwara-Moritani reaction. The versatility of this operator-friendly approach was demonstrated by a broad substrate scope which includes arenes, heteroarenes and a variety of olefins. Electroanalytical studies suggest the involvement of a Pd(ii)/Pd(iv) catalytic cycle via a Pd(iii) intermediate.
ABSTRACT
Fluorine compounds are known for their abundance in more than 20% of pharmaceutical and agrochemical products mainly due to the enhanced lipophilicity, metabolic stability and pharmacokinetic properties of organofluorides. Consequently, the last decade has seen enormous growth in the incorporation of a trifluoromethyl group into organic motifs. With due significance, this review aims to provide a complete picture of the transition metal-mediated construction of C(sp3, sp2, and sp)-CF3 bonds via C-H/X bond functionalization or addition processes in both aliphatic and aromatic hydrocarbons. Diversified reagents ranging from radical and electrophilic to nucleophilic trifluoromethylating agents and their respective mechanisms have been further deliberated in this comprehensive overview. The comprehensive coverage on this topic is expected to make this review unique and beneficial for further future applications enriching the community towards further improvements in the field of trifluoromethylation reactions, in turn improving the propensity towards further development of agrochemical drugs.
