Papers by Sosale Chandrasekhar
International Journal of Biochemistry Research & Review, 2016
Research on Chemical Intermediates, 1992
Tetrahedron Letters, 2001
Several ketoxime hydrochlorides undergo Beckmann rearrangement upon heating below their melting p... more Several ketoxime hydrochlorides undergo Beckmann rearrangement upon heating below their melting points for 5-48 h, in excellent yields (generally >70%). The absence of a reaction solvent and of by-products (except for HCl) makes for a very simple work-up. Aldoxime hydrochlorides apparently undergo dehydration to the corresponding nitriles under the above conditions. Dibenzyl ketoxime hydrochloride unexpectedly furnished a pyrazine derivative (67%), presumably via further reaction of the intermediate nitrilium ion in the crystal lattice.
Tetrahedron: Asymmetry, 2002
Several secondary alcohols undergo the Mitsunobu reaction with triphenylphosphine, diethyl azodic... more Several secondary alcohols undergo the Mitsunobu reaction with triphenylphosphine, diethyl azodicarboxylate and (1S)-(+)-ketopinic acid (0.5 equiv. each relative to alcohol) in CH 2 Cl 2 solution at −23°C, to furnish the chiral secondary alcohol and its ketopinate ester (d.e. >95%). Chromatographic separation of these and subsequent hydrolysis of the ketopinate ester (KOH/EtOH/0°C) provides the chiral secondary alcohol in overall yields of 75% and e.e. of 80%. When the above Mitsunobu reaction is performed with 1 equiv. of all the reactants, an effective dynamic kinetic resolution of the alcohol is observed in two cases, the ketopinate esters being isolated in 63 and 75% yields and >95% d.e.
Acta Crystallographica Section C Crystal Structure Communications, 2009
Tetrahedron Letters, 2006
Azlactone anions-the key intermediates in the classical Erlenmeyer synthesis of amino acids-appar... more Azlactone anions-the key intermediates in the classical Erlenmeyer synthesis of amino acids-apparently possess aromatic stabilization, as indicated by the relative rate of base catalyzed deuterium exchange in the following analogs: 1-methyl-2-phenyl-5(4H)-imidazolone > 2-phenyl-5(4H)-oxazolone (azlactone) > 3,3-dimethyl-2-phenyl-4(3H)-pyrrolone. This is paralleled by the relative rate of condensation of these compounds with hexadeuteroacetone. Reported pK a data also suggest that the azlactone products of the Erlenmeyer synthesis are analogs of the fulvenes.
ChemInform, 2010
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was e... more ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Tetrahedron Letters, 2000
The titled reaction was eected with iso-amyl nitrite or sodium nitrite, both in conc. H 2 SO 4 at... more The titled reaction was eected with iso-amyl nitrite or sodium nitrite, both in conc. H 2 SO 4 at 0±25 C in excellent yields (55±98%). Apart from the mild temperatures employed, organic solvents and reagents can be avoided, and the by-products are CO 2 and N 2 , so the conditions are environment-friendly.
Tetrahedron: Asymmetry, 2006
Three tricyclic imides were prepared by a Diels–Alder reaction of 6-arylfulvenes and maleic anhyd... more Three tricyclic imides were prepared by a Diels–Alder reaction of 6-arylfulvenes and maleic anhydride, followed by treatment with NH3. The exo isomers were found to exist as conglomerates when the aryl group was either p-tolyl or p-anisyl (although not phenyl). Triage of the p-tolyl racemate, followed by reaction with p-toluenesulfonyl chloride in CH2Cl2/Et3N, led to the crystalline enantiopure N-tosylimides (these
Tetrahedron: Asymmetry, 2005
Ketones can be reduced with NaBH 4 in diglyme without an apparent proton source, but putatively c... more Ketones can be reduced with NaBH 4 in diglyme without an apparent proton source, but putatively catalysed by a trialkyl borate. This can be initially derived in situ from NaBH 4 and an alcohol, although the reaction becomes increasingly autocatalytic with time. With (À)-menthol as the initiating alcohol, the enantioselective reductions of a range of prochiral ketones in quantitative yields and moderate ees (generally 58-87%) were realised (the autocatalysis was demonstrated in two cases; catalysis by tris-(À)menthyl borate was demonstrated in one case). The mechanism may involve either the activation of the substrate (electrophilically) or of the hydride reagent (nucleophilically). This method offers a relatively simple and inexpensive approach to a key transformation in asymmetric synthesis.
Tetrahedron: Asymmetry, 2012
ABSTRACT Various 1-acyl-2,4,10-trioxaadamantanes were prepared from the corresponding 1-methoxyca... more ABSTRACT Various 1-acyl-2,4,10-trioxaadamantanes were prepared from the corresponding 1-methoxycarbonyl derivatives, via conversion to the N-acylpiperidine derivatives followed by reaction with a Grignard reagent in refluxing THF. These α-keto orthoformates were converted to the corresponding imines with 1-(S)-phenethyl amine (TiCl4/Et3N/toluene/reflux), with the Schiff bases being reduced further with NaBH4 (MeOH/0 °C) into the corresponding 1-(S)-phenethyl amines (diastereomeric excess 91:9 by NMR). Hydrogenolysis of the phenethyl group (Pd-C/MeOH) finally led to the 1-(aminoalkyl)trioxaadamantanes, which are chiral C-protected α-amino acids, in excellent overall yields.
Tetrahedron: Asymmetry, 2000
(1S,5R,7R)-(^)-10,10-Dimethyl-3-ethyl-4-oxa-2-azatricyclo[5.2.1.0 1,5 ]dec-2-ene 2 was prepared i... more (1S,5R,7R)-(^)-10,10-Dimethyl-3-ethyl-4-oxa-2-azatricyclo[5.2.1.0 1,5 ]dec-2-ene 2 was prepared in 95% yield from (1S)-1-amino-2-exo-hydroxyapocamphane 1. The chiral oxazoline could be alkylated (LDA/ THF/^78 C/RX, RX=ethyl, n-propyl, n-butyl iodides or benzyl bromide) to 3 in 95% yield and >95% diastereoselectivity, and the products hydrolysed to (R)-2-methylalkanoic acids 4 (43±47% yield, 93±98% e.e.).
Tetrahedron Letters, 1987
An intramolecular Baeyer-Villiger reaction has been effected involving a conformationally-fixed i... more An intramolecular Baeyer-Villiger reaction has been effected involving a conformationally-fixed intermediate which breaks down with stereoelectronic control.
Tetrahedron Letters, 2007
Oxazole derivatives R 0220 Erlenmeyer Azlactone Synthesis with Aliphatic Aldehydes under Solvent-... more Oxazole derivatives R 0220 Erlenmeyer Azlactone Synthesis with Aliphatic Aldehydes under Solvent-Free Microwave Conditions.-A successful extension of the title reaction in a novel microwave-induced solvent-free process is described.-(CHANDRASEKHAR*, S.;
Research on Chemical Intermediates, 2002
A simple thermodynamic analysis of the well-known Michaelis-Menten equation (MME) of enzyme catal... more A simple thermodynamic analysis of the well-known Michaelis-Menten equation (MME) of enzyme catalysis is proposed that employs the chemical potential ¹ to follow the Gibbs free energy changes attending the formation of the enzyme-substrate complex and its turnover to the product. The main conclusion from the above analysis is that low values of the Michaelis constant K M and high values of the turnover number k cat are advantageous: this supports a simple algebraic analysis of the MME, although at variance with current thinking. Available data apparently support the above ndings. It is argued that transition state stabilisation-rather than substrate distortion or proximity-is the key to enzyme catalysis.
Research on Chemical Intermediates, 1998
It is proposed that molecular phenomena may only be described within the framework of the Complem... more It is proposed that molecular phenomena may only be described within the framework of the Complementarity Principle ('CP'), and that scientific controversy may originate in the essential incompatibility of complementary representations. Complementarity based on the temporal Uncertainty Principle leads to new insights into transition state theory, microscopic reversibility and the Curtin-Hammett Principle. An empirical application of the 'CP' to the structural theory leads to a revision of present concepts of 'reaction dynamics', with the Principle of Least Nuclear Motion ('PLNM') emerging as a general alternative to electronic theories of reactivity. In fact, it is argued that the 'PLNM' is a better basis for the Woodward-Hoffmann rules than is orbital symmetry. A more flexible approach to organic reaction mechanisms is thus indicated. Also, as the basis of the structural theory is fundamentally uncertain, and the present theory of X-ray diffraction apparently incompatible with the 'UP', a reinterpretation of the Bragg equation has been attempted.
Journal of Chemical Research, 2001
A set of four fulvenes bearing both electron-withdrawing and -donating aryl groups at C6 was prep... more A set of four fulvenes bearing both electron-withdrawing and -donating aryl groups at C6 was prepared and shown to be fairly stable, except for the dimerisation of the anisyl-nitrophenyl-fulvene 1a, which also underwent a (4π + 2π) cycloaddition with C,N-diphenylnitrone.
Chirality, 2007
Previous proposals for the origin of molecular homochirality, based on the effect of the weak neu... more Previous proposals for the origin of molecular homochirality, based on the effect of the weak neutral current (WNC) on enantiomers, and the amplification of the resultant parity‐violating energy difference (PVED), are possibly flawed. The additive amplification of PVED in crystals and polymers (“Yamagata hypothesis”) cannot lead to detectable levels of optical activity, the original theory apparently overestimating PVED by a factor equal to Avogadro's number. An alternative theory based on the irreversible and spontaneous evolution of a dynamically fluctuating system is apparently impractical. However, the nonlinear amplification of PVED via autocatalytic polymerization may be possible as indicated by a simplified physico‐chemical approach. This may also occur during crystallization and melting, and form the basis of the second order asymmetric transformation. (Thus, reported differences in the melting points of enantiomers in several cases may well be real). Also, the preponder...
Journal of the Chemical Society, Perkin Transactions 1, 1975
This rearrangement occurs in good yield on irradiation of ethanolic solutions, but 2-methylcinnol... more This rearrangement occurs in good yield on irradiation of ethanolic solutions, but 2-methylcinnolinium-4-thiolate, 1-methyl-4(1H)-cinnolone, and 2-methyl-3(2H)-cinnolone do not react.
Uploads
Papers by Sosale Chandrasekhar