Umpolung Reactivity of Diazo Arylidene Succinimides: Distal C-H Functionalization of α-Thiocarbonyls from the Reactive Carbenoid Center.

Herein, for the first time we have explored the umpolung reactivity of the vinylogous carbon center of diazo arylidene succinimide (DAS) through rhodium catalysis to achieve [2,3]-Stevens rearrangement of α-thioether esters. The protocol has successfully demonstrated the distal C-H bond functionalization of the α-thioether esters. Alongside, the carbenoid reactivity of DAS has also been achieved with Doyle-Kirmse reaction of allyl/propargyl phenyl sulfides. The protocol proved to be practical to synthesize a wide variety of [2,3]-Stevens rearrangement products exclusively and the possible side products emanating from Pummerer rearrangement and [1,2]-Stevens rearrangement were not observed. This catalytic protocol works smoothly in environmentally benign solvent under open air to afford the corresponding desired products with excellent diastereo-, regio- and chemo-selectivities in good to excellent yields. The protocol also proved to be scalable on gram quantity.

Highly Site-Selective Direct C-H Bond Functionalization of Unactivated Arenes with Propargyl α-Aryl-α-diazoacetates via Scandium Catalysis.

Highly chemo- and regio-selective C-H bond functionalization of unactivated arenes with propargyl α-aryl-α-diazoacetates has been developed using scandium catalysis. A variety of unactivated, mildly deactivated, and electronically activated arenes have been functionalized using this protocol. The synergistic combination of scandium triflate as a catalyst and propargyl α-aryl-α-diazoacetate as a reagent played a pivotal role in the effective C-H bond functionalization of arenes without the assistance of any directing group or ligand. The practicality of the protocol has been demonstrated by the gram-scale synthesis of very useful α,α-diarylacetates including antispasmodic drug-adiphenine. Based on the experimental observations, labeling experiment, and density functional theory calculations, a plausible reaction mechanism has been outlined.

De novo protecting-group-free total synthesis of (+)-muricadienin, (+)-ancepsenolide and (+)-3-hexadecyl-5-methylfuran-2(5H)-one.

A de novo protecting-group-free total synthesis of (+)-muricadienin, (+)-ancepsenolide and (+)-3-hexadecyl-5-methylfuran-2(5H)-one has been achieved. Ring-closing-metathesis has been the key step in the synthesis. In (+)-muricadienin synthesis, a long chain alkyl group has been installed by an sp-sp3 Sonogashira type reaction followed by a cis-selective Lindlar reduction. The total synthesis is achieved in 7 steps and in excellent 43.5% overall yield. Similarly, (+)-ancepsenolide and (+)-3-hexadecyl-5-methylfuran-2(5H)-one synthesis is completed in 5 steps each and in 48 and 68% overall yields, respectively.