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  • Open access
  • 63 Reads
DTBB-Catalysed Lithiation of Cis- and Trans-2,3-diphenyloxirane Gives the Same Organolithium Intermediate
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The reaction of cis- or trans-2,3-diphenyloxirane with lithium powder and a catalytic amount of 4,4’-di-tert-butylbiphenyl (DTBB, 5% molar) in the presence of 3-pentanone as electrophile in THF at temperatures ranging between –90 and –50ºC gives, after hydrolysis with water, the corresponding 1,3-diol 5 with the same stereochemistry (1S*,2R*) independently of the geometry of the starting oxiranes. A mechanistic explanation for this behaviour is given.
  • Open access
  • 57 Reads
Enantiospecific Preparation of 10-(pyperidin-1-yl)Camphor: A Model Procedure for 10-Aminocamphors
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Enantiopure (1R)-10-(pyperidin-1-yl)camphor has been straightforwardly obtained from natural camphor in five individual steps and with a high overall yield. The process involves a stereocontrolled double-Wagner-Meerwein-rearrangement strategy to generate 10-(triflyloxy)camphor as the key intermediate. This peculiarly-stable neopentylic-like triflate is able to react with pyperidine easily and without producing Grob-like fragmentation of the b-(triflyloxy)ketone-based norbornane system. The described procedure constitutes a model procedure for the sterecontrolled preparation of interesting 10-aminocamphors.
  • Open access
  • 69 Reads
Synthesis and Spectral Properties of Heterocycles as 2H-2-chromenone Derivatives
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3-Aryl-2H-2-chromenehydrazones react with isothiocyanates to form 3-aryl-2H-2-chromene thiosemicarbazones, which exist in tautomeric equilibrium in DMSO-d6 solution. 3-R’-2-(3-aryl-2?-2-chromenylideneazo)-4-thiazolidinones were obtained by cyclocondensation of 3-aryl-2H-2-chromene thiosemicarbazones with ester of bromoacetic acid in the presence of sodium acetate. 1-(2H-2-Oxochromen-6-yl)-4-phenyl thiosemicarbazide was obtained in the same manner from 2H-2-oxochromen-6-yl hydrazine. The interaction of C-4-nitrophenyl-N-3-nitrophenylnitron with 1-(2-oxo-2H-1-benzopyran-6-yl)-1H-pyrrole-2,5-dione leads to [3+2] cycloaddition products as mixture of stereoisomers.
  • Open access
  • 49 Reads
A New Approach to the Synthesis of Biginelli Compounds and Their Analogues
A new synthesis of esters of 2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxylic acids and some related compounds has been developed. The synthesis is based on reaction of a-tosyl-substituted phenyl carbamates with enolates of b-oxoesters or 1,3-dicarbonyl compounds followed by treatment of the obtained products with ammonia and dehydration of the resulting 4-hydroxyhexahydropyrimidin-2-ones.
  • Open access
  • 40 Reads
Synthesis of 5-R-thio, 5-R-sulfinyl, 5-R-sulfonyl and 5-di(R-oxy)phosphoryl Substituted Hydrogenated Pyrimidine-2-thiones/ones
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general and efficient synthesis of hexahydro- and 1,2,3,4-tetrahydropyrimidine-2-thiones/ones bearing R-thio, R-sulfinyl, R-sulfonyl and di(R-oxy)phosphoryl groups at the C(5) is described. The key stage of the synthesis is reaction of readily available a-tosyl or a-azido substituted thioureas or ureas with enolates of the corresponding a-substituted ketones.
  • Open access
  • 64 Reads
Intramolecular 1,3-dipolar Cycloreversion - A Key Step in Novel Thermal Isomerisations of Cyclobutane Di-(carbomethoxy) Triazolines
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Thermal isomerisation of the strained cyclobutane diester triazoline led to the formation of the product possessing a novel 1,2,7-triaza-[3.3.0]octa-2-ene ring system incorporated in a norbornane framework. Experimental evidence and quantum chemical calculations (DFT) have been used to support a postulated reaction mechanism involving as the first step, a rare example of intramolecular 1,3-dipolar cycloreversion. Subsequently, several steps involving 1,3-dipolar ring closure, [1,3]hydrogen-shifts and an intramolecular addition are postulated leading to the observed product of this deep-seated isomerization. The influence of changing substituents on the product outcome of this novel reaction cascade was also studied.