The intramolecular photorearrangement of cyclopentones

Synthesis of 4,5,9,10-tetradehydroadamantan-2-one

“…A conventional method for the homologation of ketones is the Evans modification' of the Tiffeneau-Demjanov procedure. 8 In this approach, a ketone is converted in two steps to the corresponding P-aminomethyl alcohol, which is then treated with nitrous acid. However, the reported homologations of several bicyclic and polycyclic ketones by this method show a significant preference for insertion of the new skeletal carbon between the carbonyl carbon and the less substituted adjacent carbonag Particularly distressing in this regard was the observation by Hall that ring expansion of 10 upon reaction with nitrous acid gives 11 in greater than 90% purity.1° In striking contrast to these results, Knapp and his coworkers have recently reported a method for the regiospecific homologation of 2-norbornanone which proceeds by exclusive migration of the more substituted carbon."…”

Photochemical ring expansion of cyclic aliphatic ketones. Cyclobutanones and cyclopentanones

“…For 37: nmr (CC14) 8.35 (m, 12), 5.23 (m, 1, acetal ), 4.08 (m, 1, vinyl H); ir jw 1695, 1160, 1040, 976 cm-1. For 36: nmr (CC14) 9.03, 9.00, 8.96 (3 s, 12), 8.36 (m, 6), 7.17 (s, 1), 5.86-6.79 (m, 2), 5.53 (s, 1); ir 1372, 1351, 1143, 1130, 1087 (s), 1035 (s), 966 (s), 911, (s) cm'1. For 35 (both cis and trans isomers eluted as a single peak): nmr (CC14) 9.08, 9.01, 8.98, 8.94, 8.88, 8.83, 8.75, 8.72., 8.70 (10, s, 12 H total); 8.36 (bd m, 6 H); 6.75 (s, OCH, cis-35); 6.73 (s, OCH3 tra«í-35)(3,Htotal); 6.51 (bd m), 6.21 (s); 6.12 (s), 6.9-S.9 (bd m) (3 H total), 5.78, 5.75 (2s, 1 H, THF acetal (proton); 5.48 (bd m, 1 , acetal proton); ir rw 1379, 1362, 1135, 1121, 1096 (s), 1079 (s), 1030 (vs), 972 (s) cm-1.…”

“…Studies have revealed that 3 is most efficiently trapped by alcohols to afford ring expanded acetals 4 as isolable products. [5][6][7] In this report, we present additional results from our investigation of the photochemical ring expansion reaction of cyclic aliphatic ketones and suggest a somewhat modified mechanism which is capable of explaining a variety of reported results.…”

Photochemical reactivity of keto imino ethers

“…There are, however, several examples in the literature of related systems which a-cleave. 2-Cyclopentenones substituted in the 5 position (35) preferentially a-cleave in dilute solution to give cyclopropy ketenes(36) among other products as observed by Agosta, Kende, and co-workers 36). These reactions have been shown to occur under sensitized conditions, but the details of the mechanism are still unknown.…”