Ca(II)-Catalyzed Regioselective Cascade Synthesis of Oxindolyl- Naphthofurans through Meyer-Schuster type Rearrangement

Enantioselective synthesis of 3-hydroxy- and 3-amino-3-alkynyl-2-oxindoles by the dimethylzinc-mediated addition of terminal alkynes to isatins and isatin-derived ketimines

A common protocol for enantioselective alkynylation of isatins and isatin-derived ketimines using terminal alkynes and Me2Zn in the presence of a catalytic amount of a chiral perhydro-1,3-benzoxazine with moderate to excellent enantioselectivity under mild reaction conditions is described. The additions to ketimines present a novel approach to chiral amines being derivatives of oxindoles. The reaction is broad in scope with respect to aryl- and alkyl-substituted terminal alkynes and isatin derivatives. In isatins, the alkynylation occurs at the Si face of the carbonyl group, whereas in the ketimine derivatives it occurs at the Re face of the imine.

Stereoselective sulfenylation of oxindole-derived propargyl alcohols to access sulfenylated-3-alkenyloxindoles

A Ca-catalyzed, tetrasubstituted alkenyl-sulfenylation was achieved using readily available aryl/alkyl thiols and easily prepared oxindole-derived propargyl alcohols under solvent-free conditions. The reaction proceeded with hydrogen bonding assisted regioselective α-thiolation and subsequent calcium catalyzed stereoselective alkenylation to yield E-alkenyl thioethers with high diastereoselectivity.

Calcium-catalyzed formal [3 + 2] annulation of C,N-diacyliminium ions with nucleophilic phenols: a diversity oriented synthesis of 3-aminofurans

We have developed a one-pot, three-component, and solvent-free reaction for the synthesis of 3-aminofurans using a calcium catalyst. In this cascade reaction, the key intermediate, C,N-diacyliminium ion, is formed in situ from glyoxal and lactam, which further reacted with phenolic nucleophiles to form furan derivatives in good yields with broad substrate diversity. We also present here the preliminary photophysical studies of selected compounds.

Recent advances in alkaline earth metal-enabled syntheses of heterocyclic compounds

This review summarizes recent progress in alkaline earth metal enabled syntheses of heterocyclic compounds.

Regiospecific formal [3 + 2] annulation of tert-propargyl alcohols with acyclic 1,3-diketones via the cycloisomerization of homoallenyl ketones

A one-pot, regiospecific synthesis of dihydrofurans bearing a quaternary centre is developed from the formal [3 + 2] annulation of tert-propargyl alcohols and 1,3-diketones through the S_N2^I mechanism to form homoallenyl ketone and a subsequent cycloisomerization reaction.

Highly Regioselective Synthesis of Oxindolyl-Pyrroles and Quinolines via a One-Pot, Sequential Meyer-Schuster Rearrangement, Anti-Michael Addition/C(sp3)-H Functionalization, and Azacyclization

A one-pot, sequential Meyer-Schuster (MS) rearrangement of oxindole-derived propargyl alcohols to the corresponding α,β-unsaturated enones and their anti-Michael addition, followed by intramolecular azacyclization is described in a highly regioselective manner using Ca(OTf)₂ as the promoter. Further, we described the one-pot MS rearrangement, followed by C_(sp³)-H functionalization of 2-methyl azaarenes at α-carbon of these doubly activated alkenes. Control experiments and computational calculations were performed to propose the reaction mechanism.