A comparison of the photoaddition reactions of nucleic acid nitrogen bases and cyclohexenones with isobutylene. The role of rigidity in product formation

Urocanic Acid Photochemistry and Photobiology

“…4). There are ample precedents for the excited state of DMT to react through photocycloaddition, both to another DMT molecule (73) as well as to other olefins (127,128). However, the UA excited state is also known to photodimerize, albeit only in the solid state (50).…”

Deuterated and partially deuterated polyisobutenes, synthesized via living carbocationic polymerization

“…As a consequence several authors used methylenebismagnesium halides instead of methylenetriphenylphosphorane to synthesize terminally deuterated olefins 36) , including isobutenes 37,38) . However, the exchange reactions reported in the case of the Wittig synthesis involve hydrogen and deuterium atoms bound to either carbon atoms in a-position to the carbonyl group or to the carbon atom connected to the phosphorus of the phosphorane.…”

Enone Photochemical Cycloaddition in Organic Synthesis

“…(3 I) It has also been reasoned that the first bond is formed at the a position in an attempt to explain the regiochemistry of enone cycloaddition(32.33); however, no evidence has been produced to support this, and the intermediacy of exciplexes can rationalize the observed regiochemistry satisfactorily, as will be discussed below. The frequent observation of olefinic products which appear to be derived from bonding to both the a position and the /3 position (e.g., (34) structures 2 and 3 in Scheme 6) indicates that in all probability the initial bonding can be at both positions with the relative proportions depending upon the structures of the enone and alkene involved. The relative efficiencies of enone cycloadditions with olefins of varying structure have been compared.…”