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Selektivitäten bei Photoadditionen an multifunktionelle Coffein‐Derivate
Author(s) -
Kaupp Gerd,
Ringer Ernst
Publication year - 1991
Publication title -
chemische berichte
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 0009-2940
DOI - 10.1002/cber.19911240215
Subject(s) - chemistry , diradical , double bond , hydrolysis , medicinal chemistry , stereochemistry , propellane , bicyclic molecule , excited state , organic chemistry , singlet state , physics , nuclear physics
Selectivities in Photoadditions with Multifunctional Caffeine Derivatives Electronically excited stilbene ( 21* ), 4,4′‐dichlorostilbene ( 1* ), and 4,4′‐dimethoxystilbene ( 18* ) are trapped by caffeine derivatives 2, 13 , or 22 with variable results. While 1* and 2 react predominantly at the imino double bond (substitutive and fragmentating additions), 1* or 18* and 13 produce mostly propellanes by [2 + 2] photocycloaddition, which hydrolyze or may be hydrolyzed. 21* and the relatively electron‐poor compound 22 produce mostly propellanes, which always show a preponderance of the syn ‐10, anti ‐11 stereoisomers. These selectivities as well as the competition with reactions at the imino double bonds are rationalized on the basis of diradical mechanisms with the aid of semiempirical AM1 calculations. Earlier results on closely related transformations are also discussed.