Conformational analysis of 2-(diphenylphosphinoyl)-tetrahydrothiopyran: Lack of additivity of the S-C-P anomeric effect

✍ Scribed by Mario Ordóñez; Eusebio Juaristi

• Book ID: 104208298
• Publisher: Elsevier Science
• Year: 1998
• Tongue: French
• Weight: 365 KB
• Volume: 54
• Category: Article
• ISSN: 0040-4020
• DOI: 10.1016/s0040-4020(97)10374-x

✦ Synopsis

The conformational preference of the diphenylphosphinoyl group at the alpha position in the thiane ring was estimated by low temperature NMR, AG~raK = + 0.46 + 0.11 kcal/mol, and at 50°C, via chemical equilibration 0 of anancomeric models, AGa2aK = -0.26 +_ 0.10 kcal/mol. These thermodynamic data allowed the estimation of the enthalpic and entropic contributions to the axial ~ equatorial conformational equilibrium of 2-(diphenylphosphinoyl)thiane, AH ° = + 1.29 + 0.12 kcal/mol, and AS ° = + 4.8 + 0.7 cal/K.mol. Comparison of the enthalpic S-C-P(O) anomeric effect in the thiane and 1,3-dithiane systems, 2.68 versus 3.39 kcal/mol, respectively, leads to the conclusion that no additivity of the S-C-P(O) anomeric effect takes place.