The Fujiwara-Moritani reaction has had a profound contribution in the emergence of contemporary C-H activation protocols. Despite the applicability of the traditional approach in different elds, the associated reactivity and regioselectivity issues had rendered it redundant. The revival of this exemplary reaction requires the development of a mechanistic paradigm that would have simultaneous control on both the reactivity and regioselectivity. Often high thermal energy required to promote ole nation leads to multiple site functionalization. To this aim we established a photoredoxcatalytic system constituting a merger of palladium/organo-photocatalyst that forges oxidative ole nation in an explicit regioselective fashion of diverse arenes and heteroarenes. Visible light plays a signi cant role in executing 'regio-resolved' Fuijiwara-Moritani reaction without the requirement of silver salts and thermal energy. The catalytic system is also amenable towards proximal and distal ole nation aided by respective directing groups (DGs), which entails the versatility of the protocol in engaging the entire spectrum of C(sp2)-H ole nation.Furthermore, streamlining the synthesis of natural products, chiral molecules, drugs and diversi cation through late-stage functionalizations underscore the importance of this sustainable protocol. The photoinduced attainment of this regioselective transformation is mechanistically established through control reactions, kinetic studies and theoretical calculations.
Biaryl scaffolds are found in natural products and drug molecules and exhibit a wide range of biological activities. In past decade, the transition metal-catalyzed C–H arylation reaction came out as an effective tool for the construction of biaryl motifs. However, traditional transition metal-catalyzed C–H arylation reactions have limitations like harsh reaction conditions, narrow substrate scope, use of additives etc. and therefore encouraged synthetic chemists to look for alternate greener approaches. This review aims to draw a general overview on C–H bond arylation reactions for the formation of C–C bonds with the aid of different methodologies, majorly highlighting on greener and sustainable approaches.
Despite the widespread applications of C–H functionalization, controlling site selectivity remains a significant challenge. Covalently attached directing groups (DGs) served as ancillary ligands to ensure ortho-, meta- and para-C–H functionalization over the last two decades. These covalently linked DGs necessitate two extra steps for a single C–H functionalization: introduction of DG prior to C–H activation and removal of DG post-functionalization. Here we report a temporary directing group (TDG) for meta-C–H functionalization via reversible imine formation. By overruling facile ortho-C–H bond activation by imine-N atom, a suitably designed pyrimidine-based TDG successfully delivered selective meta-C–C bond formation. Application of this temporary directing group strategy for streamlining the synthesis of complex organic molecules without any necessary pre-functionalization at the meta position has been explored.
Methods to selectively functionalize any one sp 3 CÀ H bond among all others, has been well documented in literature. Radical reactions, which are essentially mild reaction conditions has provided a significant improvement over the standard functionalization pathways. Although radical recombinations are fast and feasible, the selectivity is always guided by the electronic biasness in the system. 1,n-Hydrogen atom transfer (HAT) reactions are extremely useful in determining regioselectivity, the involvement of a 1,5-HAT protocol made the reaction pathway energetically much more favourable to functionalize the desired remote C(sp 3 )À H bond. In this review we are going to give a brief overview of the methods involved in the functionalization of distal aliphatic CÀ H bond by 1,5-HAT transformation pathway.Scheme 5. Homolyzation of amide NÀ H bond to trigger 1,5-HAT using iridium photocatalyst. Scheme 6. Rh-catalyzed asymmetric HLF type reaction.
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