Issue in Honor of Prof. B. S. Thyagarajan ARKIVOC 2001 (xi) 1-11 Scheme 2 At USC, Thyagarajan developed a photochemical route to the cyclization of benzanilide, anilide and phenanthridione analogs (Scheme 3).12 He showed that the iodoaryl intermediate (on either end of the amide) preceded aryl coupling by independently preparing each isomer and demonstrating the conversion of each to the biaryl product. This work was the first demonstration of the photocyclization of benzanalide compounds. Scheme 3 Heterocyclic chemistry. Thyagarajan published multiple mechanistically interesting and novel pathways to heterocycles and contributed an important review on aromatic quinozilines.13 He and Glaspy discovered that acetylenic derivatives with non-geminal propargylic thiophenyl and Nalkylamino units undergo rearrangements to N-arylpyrroles with concomitant extrusion of thiophenol (scheme 4).13 The authors invoked a 1,3-arylthio shift to the allene followed by a rearrangement to generate a vinyl aziridine. The known vinyl aziridine-type cyclization led to ring expansion to the target compound. Scheme 4 Organic reaction mechanisms. During his collaborations with Zimmerman at Northwestern University, Thyagarajan made significant contributions to understanding the stereoelectronic effects of the proton transfer reactions of sulfonyl anions. Thyagarajan and Zimmerman discovered that the kinetic protonation of the carbanions derived from 1-phenylsulphonyl-2phenylcyclohexane generated trans products, in sharp contrast to the cis products generated from the nitro and benzoyl analogs (scheme 5).14 This selectivity was exhibited irrespective of initial stereochemistry, counterion, or solvent. The protonation stereoselectivity, however, was ISSN 1424-6376 Page 4 ©ARKAT USA, Inc 0
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