Synthesis of bicyclic cyclopentanols by photoreductive cyclization of .delta.,.epsilon.-unsaturated ketones

Formation of a Five‐Membered Ring

“…For example, the irradiation of acetylenic ketoester 218 either in HMPA or Et 3 N/CH 3 CN afforded the allylic bicyclic alcohol 219 as the exclusive product in high yield (Scheme 8.60). Similarly, when allenic compound 220 was irradiated in Et 3 N/ CH 3 CN, it afforded the cyclized products 221 and 222, in 55% and 20% yield, respectively [99].…”

Radical ion cyclizations

“…Intensive studies concerning the photoreductive cyclization of distinct ketones and aldehydes are made by Cossy et al [170]. They describe how bicyclic tertiary cycloalkanols 173 and 174 can be prepared from 6,e-unsaturated ketones 172 in good yields, initiated by photoinduced electron transfer from triethylamine in acetonitrile or by photoionization in pure hexamethylphosphoric triamide (HMPA) [171,172]. The reaction is stereo-, chemo-and …”

“…Electroreductive cyclization of ketone 213, with the length of the allenic side chain shortened, leads to kinetically stable endo-ene bicyclic alcohol 212, whereas chemical reduction produces thermodynamically stable exo-ene bicyclic alcohol 214. Similar compounds have successfully been cyclized under PETreductive conditions, yielding 5-exo products containing the double bond in endo-and exocyclic positions with some preference for the former [172] (Scheme 41).…”

A new diastereoselective intramolecular electroreductive coupling of unsaturated β-ketoesters and β-ketoamides in ionic liquids at a tin cathode

“…We have reported earlier enantioselective 16 syntheses of (S)-alcohols from ketones at a mercury cathode in DMF-water (90:10) using a catalytic amount of (1R,2S)-(À)-N,N-dimethylephedrinium tetrafluoroborate. The reductive cyclization of several unconjugated ketones, for example, 6-heptan-2-one, was accomplished with excellent regio-and stereochemical control 1,2,4,5,8 leading to the formation of (1R,2S)-1,2-dimethylcyclopentanol.These reactions involve hazardous chemicals, for example, solvents such as dimethylformamide and tetrahydrofuran and mercury as the cathode. The development of ecofriendly 'green' alternatives to common organic solvents has attracted enormous interest worldwide and ionic liquids (ILs) 17 fall into this domain.…”

“…We have reported earlier enantioselective 16 syntheses of (S)-alcohols from ketones at a mercury cathode in DMF-water (90:10) using a catalytic amount of (1R,2S)-(À)-N,N-dimethylephedrinium tetrafluoroborate. The reductive cyclization of several unconjugated ketones, for example, 6-heptan-2-one, was accomplished with excellent regio-and stereochemical control 1,2,4,5,8 leading to the formation of (1R,2S)-1,2-dimethylcyclopentanol.…”