Department of Chemistry
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Item Microwave-Accelerated Solvent-Free Synthesis of Thioketones, Thiolactones, Thioamides, Thionoesters, and Thioflavonoids(RSC, 1999-07-29) Kumar, DalipAn expeditious, solvent-free, and high yield conversion of ketones, flavones, isoflavones, lactones, amides, and esters to the corresponding thio analogues is described utilizing Lawesson's reagent in a process that circumvents the use of dry solvents and excess of the reagent.Item Synthesis and Thermolysis of Heterocyclic 3-Aza-3-ene-1,5-diynes(ACS, 2002-11-12) Kumar, DalipSimple, acyclic 3-aza-3-ene-1,5-diynes undergo an aza-Bergman rearrangement to a fleeting 2,5-didehydropyridine (2,5-ddp) intermediate that rapidly ring-opens to β-alkynylacrylonitrile products. In an effort to access longer-lived 2,5-ddp intermediates, we have prepared heterocyclic 3-aza-3-ene-1,5-diynes. The thermolysis of one such heterocyclic aza-enediyne does not afford products derived from trapping a 2,5-ddp intermediate but rather cyclopropanes that appear to arise from a carbene intermediate and a product that appears to be a trapping product from a 2,3-ddp intermediate.Item An Extremely Facile Aza-Bergman Rearrangement of Sterically Unencumbered Acyclic 3-Aza-3-ene-1,5-diynes(ACS, 2003-02) Kumar, DalipThe factors that affect the kinetics of the aza-Bergman cyclization of aza-enediynes (C,N-dialkynyl imines) have not previously been elucidated. Here we report our kinetic studies of the aza-Bergman reactions of a series of 6-triisopropylsilyl and 6-unsubstituted 1-phenyl-4-aryl-3-aza-3-ene-1,4-diynes in which the aryl group is phenyl, o-(methoxy)phenyl, or p-(methoxy)phenyl. These aza-enediynes are prepared as single isomers in modest yield from the corresponding 1-aryl-3-(triisopropylsilyl)propynone oximes. These aza-enediynes undergo aza-Bergman reaction followed by a rapid retro-aza-Bergman cyclization to afford β-alkynyl acrylonitrile products. In no case are products corresponding to trapping the intermediate 2,5-didehydropyridine diradical isolated. While the rate of aza-Bergman cyclization is not greatly affected by the nature of the 4-aryl substituent, the rate is very dependent on the nature of the 6-substituent. 1-Phenyl-4-aryl-3-aza-3-ene-1,5-diynes that lack a 6-substituent undergo aza-Bergman cyclization spontaneously at 20 °C with first-order half-lives of 36−78 min. The effect of solvent on the kinetics of aza-Bergman cyclization of 1,4-diphenyl-3-aza-3-ene-1,5-diyne was investigated. The rate of this cyclization is solvent dependent, proceeding more rapidly in less polar solvents.Item Synthesis of aza-fused isoquinolines through domino cross-aldol condensation and palladium-catalyzed intramolecular direct arylation(ACS, 2014) Kumar, Dalip; Kumar, AnilA straightforward method has been developed for the synthesis of aroyl-substituted imidazo-/benzimidazo-fused isoquinolines. The cascade reaction proceeds via a cross-aldol condensation of 2-(1H-imidazol-1-yl/benzimidazolyl-1-yl)-1-arylethanones and 2-bromobenzaldehyde followed by palladium-catalyzed intramolecular C–H functionalization. This approach offers a simple and efficient alternative one-pot protocol for the assembly of imidazo/benzimidazo[2,1-a]isoquinolines in moderate to good yields.Item Au-Catalyzed Synthesis of Thiopyrano[2,3-b]indoles Featuring Tandem Rearrangement and Hydroarylation(ACS, 2017) Kumar, Anil; Kumar, DalipGold(III)-catalyzed synthesis of 14-π electron heteroaromatic thiopyrano[2,3-b]indole is reported using conjugated enyne tethered indole sulfides, featuring skeletal rearrangement conjoined with intramolecular hydroarylation (via C3–H functionalization of the indole core) and oxidative aromatization. Subsequent Pd-catalyzed C–C coupling resulted in a 16-π electron heteroaromatic isothiochromeno[1,8,7-bcd]indole.