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Sulfene−Pyridine Adducts: Lewis Acid/Base Complexes, Ylides, Pyridinium Sulfinate Zwitterions, or Carbene Ylide/SO 2 Complexes?
Author(s) -
Bucher Götz
Publication year - 2003
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200300292
Subject(s) - chemistry , adduct , pyridine , pyridinium , carbene , ylide , lewis acids and bases , medicinal chemistry , photochemistry , organic chemistry , catalysis
The reactions between a number of sulfenes and pyridine have been investigated by both density functional and ab initio theory. Two reaction channels were found. Addition of pyridine to the sulfene S atom produces products with the character of Lewis acid/base adducts. In polar solvents such as acetonitrile, scipcm calculations predict a shortening of the S−N bond with increasing ylide character, as revealed by long‐wavelength absorptions predicted by time‐dependent DFT calculations. Addition of pyridine to the sulfene C atom affords adducts better described as Lewis acid/base adducts between carbene pyridine ylides and SO 2 rather than as pyridinium sulfinate zwitterions. Again, scipcm calculations predict tighter binding in polar solvents. In the series of sulfene‐pyridine adducts investigated, the C‐bound adduct was consistently lower in energy than the S‐bound adduct, by at least 15 kcal/mol. For the formation of the C‐bound adducts an activation enthalpy of 14 kcal/mol or larger is calculated, while the formation of S‐bound sulfene−pyridine adducts is predicted to proceed without any barrier. The S‐bound adducts are therefore formed in kinetically controlled reactions, while the C‐bound adducts are the thermodynamically favored products. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)