Diastereoselective Cascade Double Michael Addition to Access Bridged Coumarins, Oxindoles and Spirooxindoles: A Sustainable Strategy for Synthesis of Anticancer Molecules.

An efficient and concise synthesis of highly functionalized bridged coumarins has been developed through a diastereoselective double Michael addition reaction of p-quinols with various 4-hydroxy coumarins under catalyst-free conditions in H2O-DMSO (8:2). The method has been applied to oxindoles for the synthesis of a variety of bridged-oxindoles and bridged-spiroxindoles in presence of a DABCO base using H2O-EtOH (8:2) as solvent medium. The strategy is simple, highly atom economical as there is no by-product and environmentally benign (E-factor = 0.

N-Protection Dependent Phosphorylation of Dehydroamino Acids to Build Unusual Phosphono-Peptides.

An efficient Mn(III)-promoted phosphorylation of dehydroalanine (Dha) has been developed to give unusual α-amino acids bearing phosphonates/phosphine oxides and β-vinyl phosphonates/phosphinates depending on N-protection of amino acid. N,N-diprotected dehydroalanine reacted with H-phosphonates and H-phosphine oxides to give structurally diverse phosphorylated α-amino acids through conjugate addition of phosphorous radical generated by Mn(OAc).2HO.

Decarboxylative [3 + 2] cycloaddition of propargyl cyclic carbonates with ,-bis(nucleophile)s to access dihydrofuro[3,2-]coumarins and dihydronaphtho[1,2-]furans with quaternary center.

The development of efficient and straightforward strategies for obtaining chiral complex molecules from readily available starting materials is of great value in drug discovery. The stereodivergent synthesis of heterocycles bearing quaternary centers remains a challenge due to inherent steric issues. Herein, we report an enantioselective copper-catalyzed decarboxylative [3 + 2] cycloaddition of propargyl cyclic carbonates/carbamates with 4-hydroxycoumarins to afford a wide range of dihydrofuro[3,2-]coumarins in excellent yields and enantioselectivity.

Rh-Catalyzed Twofold Conjugate Addition of 2-Arylimidazo[1,2-]pyridines to -Quinols To Access Bridged Scaffolds with Three Contiguous Stereocenters.

A Rh(III)-catalyzed annulation of 2-arylimidazo[1,2-]pyridines with -quinols has been realized, leading to bridged heterocycles with three contiguous stereocenters via a twofold conjugate addition. The cascade reaction is diastereoselective and proceeds through a sequential Rh-catalyzed C(sp)-H functionalization of the aryl group of imidazo[1,2-]pyridine with -quinol followed by an intramolecular conjugate addition to provide a series of diverse, novel bridged heterocycles.