Diversity-Oriented Synthesis of Oxacyclic Spirooxindole Derivatives through Ring-Closing Enyne Metathesis and Intramolecular Pauson-Khand (2+2+1) Cyclization of Oxindole Enynes

Synthesis of triazole-fused tetracyclic spirooxindole derivatives via metal-free Huisgen cycloaddition

We report an efficient, metal free method for synthesizing tetracyclic spirooxindole derivatives from N-protected isatins and propargyl bromide via Huisgen cycloaddition. This simple and practicle method provides access to spirooxindoles containing five-, six-, or seven-membered rings fused to a triazole ring.

Substrate-Controlled Diversity-Oriented Synthesis of Novel Polycyclic Frameworks via [4 + 2] and [3 + 2] Annulations of Ninhydrin-Derived MBH Adducts with 3,4-Dihydroisoquinolines

Substrate-controlled diversity-oriented synthesis of polycyclic frameworks via [4 + 2] and [3 + 2] annulations between ninhydrin-derived Morita-Baylis-Hillman (MBH) adducts and 3,4-dihydroisoquinolines under similar reaction conditions have been developed. The reaction provides diversity-oriented synthesis of a series of novel and structurally complex spiro multi heterocyclic skeletons in good yields (up to 87% and 90%, respectively) with excellent diastereoselectivities (up to >25:1 dr). In particular, the switchable [4 + 2] and [3 + 2] annulation reactions are controlled by tuning the hydroxyl protecting group on the ninhydrin-derived MBH adduct to deliver structural diverse spiro[indene-2,2'-[1,3]oxazino[2,3-a]isoquinoline] and spiro[indene-2,1'-pyrrolo[2,1-a]isoquinoline], respectively. Furthermore, the relative configuration and chemical structure of two kinds of cycloadducts were confirmed through X-ray diffraction analysis.

Oxygenated Cyclopentenones via the Pauson-Khand Reaction of Silyl Enol Ether Substrates

We report here the application of silyl enol ether moieties as efficient alkene coupling partners within cobalt-mediated intramolecular Pauson–Khand reactions. This cyclization strategy delivers synthetically valuable oxygenated cyclopentenone products in yields of ≤93% from both ketone- and aldehyde-derived silyl enol ethers, incorporates both terminal and internal alkyne partners, and delivers a variety of decorated systems, including more complex tricyclic structures. Facile removal of the silyl protecting group reveals oxygenated sites for potential further elaboration.

Zn-Catalyzed enantioselective allylation and allenylation of isatins by virtue of a proline-derived chiral ligand

An asymmetric allylation and allenylation of isatins with facile organoboron reagents was developed under the catalysis of a Lewis acid. A series of optically pure 3-allyl-3-hydroxyoxindoles and 3-allenyl-3-hydroxyoxindoles can be obtained in excellent yields (up to 99% yield) and high enantioselectivities (up to 97% ee). The possible transition state was supported by DFT calculation and the corresponding mechanism was proposed. A gram scale experiment and further functionalization of these chiral 3-hydroxyoxindoles are established.

Reagent-Based Diversity-Oriented Synthesis of Triazolo[1,5-a][1,4]diazepine Derivatives from Polymer-Supported Homoazidoalanine

Herein, we report the synthesis of skeletally different triazolo[1,5-a][1,4]diazepines starting from immobilized homoazidoalanine. After sulfonylation with 2/4-nitrobenzenesulfonyl chlorides and Mitsunobu alkylation with various alkynols, the corresponding N-substituted nitrobenzenesulfonamides were obtained. Their catalyst-free Huisgen cycloaddition provided immobilized and functionalized triazolo[1,5-a][1,4]diazepines as the key intermediates for further modification. Using the concept of diversity-oriented, reagent-based synthesis, the key intermediates were subsequently converted to heterocycles bearing [5 + 7 + 5], [5 + 7 + 6], and [5 + 7 + 7] scaffolds. Furthermore, the synthesis of spirocyclic triazolodiazepines was developed.

Stereoselective synthesis and applications of spirocyclic oxindoles

This review summaries recent synthetic developments towards spirocyclic oxindoles and applications as valuable medicinal and synthetic targets.

Rh(II)/Ag(I)-Cocatalyzed Three-Component Reaction via SN1/SN1'-Type Trapping of Oxonium Ylide with the Nicholas Intermediate

A Rh(II)/Ag(I)-cocatalyzed three-component reaction of propargylic alcohol-Co₂(CO)₆ complexes with diazo compounds and benzyl alcohols is described, which represents the first trapping process of oxonium ylides with carbocations via the S_N1/S_N1'-type pathway. This transformation provides an efficient approach for construction of dicobalt hexacarbonyl-complexed 3,3-disubstituted oxindoles. Further derivatization of the product, initiated by the deprivation of the dicobalt species, gives the 3,3-disubstituted oxindoles with the ene alkynyl group and the privileged spirooxindole-vinyldihydropyran structure.

Diversity-oriented synthesis of 17-spirosteroids

A diversity-oriented synthesis (DOS) approach has been used to functionalize 17-ethynyl-17-hydroxysteroids through a one-pot procedure involving a ring-closing enyne metathesis (RCEYM) and a Diels–Alder reaction on the resulting diene, under microwave irradiations. Taking advantage of the propargyl alcohol moiety present on commercially available steroids, this classical strategy was applied to mestranol and lynestrenol, giving a collection of new complex 17-spirosteroids.

Titanocene(III)-Mediated 5-exo-trig Radical Cyclization: En Route to Spirooxindole-Based Tetrahydrofuran and Bicyclic Lactone

The isatin core system is of immense importance due to the highly reactive prochiral C-3 position, which paves an easy way to construct large arrays of spirooxindole heterocyclic motifs. Herein, we depict an isatin-derived and 3,3'-disubstituted oxindole-appended epoxy-acrylate undergoing Cp₂Ti(III)Cl-mediated reductive oxirane-ring opening with concomitant intramolecular 5-exo-trig radical cyclization leading to tetrahydrofuran-based oxa-spirooxindole systems. The fused spirooxindole structural feature is embedded in many natural products and tends to exhibit a wide spectrum of biological activities. The presence of more than one quaternary center and the availability of multiple functional groups like hydroxyl, ester, or lactone in the resultant products expand the scope of synthetic applications of the newly acquired oxa-spirooxindole molecules.

Copper-catalyzed synthesis of spiro-indolofurobenzopyrans: tandem reactions of diazoamides and O-propargyl salicylaldehydes

An atom-economical synthesis of spiro-indolofurobenzopyrans was developed from diazoamides and O-propargyl salicylaldehydes in the presence of copper(i) thiophene-2-carboxylate in a diastereoselective manner. This methodology involves the preparation of carbonyl ylide intermediates followed by 1,3-dipolar cycloaddition with internal/external alkynes, offering a great potential for constructing biologically significant spiro-indolofurobenzopyrans, as thermodynamically controlled products, in a tandem manner.