Reductive Cyclization of Nonconjugated Acetylenic Ketones to 2- Methylenecyclopenanols

Abstract

Electroreduction of series of γ-ethynl ketones in dimethylformamide gave the cyclization products, 2-methylenecyclopentanols, as the sole product in excellent yeilds. furthermore, this electrochemical techniqe was applied to a new synthesis of bicyclic alcohols with an exocyclic double bond adjacent to a bridgehed hydroxy group.

Intramolecular reductive cyclisations using electrochemistry: development of environmentally friendly synthetic methodologies

“…The intramolecular reduction of a carbonyl group and its further coupling with unsaturated systems has been reported with non-activated carbon-carbon double [127][128][129] or triple bonds, 130 to afford the corresponding cyclic alcohols. The direct, non-catalysed process was proposed to proceed through the initial one-electron reduction of the carbonyl group, with further radical coupling on the unsaturated moiety (Scheme 41).…”

Radical ion cyclizations

“…As shown earlier by Shono et al &e-and e,(-unsaturated ketones similar to 172 also cyclize under electroreductive conditions with remarkable regio-and stereoselectivity. In a mixed solvent of methanol and dioxane or in N,N-dimethylformamide using carbon electrodes, cis isomers of exocyctic tertiary alcohols 174 are exclusively obtained in yields of 32 to 87% [176,177]. Due to the stereoselectivty and the mild conditions, the PETreductive cyclization reaction has been applied to the total synthesis of polycyclic and heterocyclic biologically active natural products such as ( + ) Hirsutene 180 [178,179] or ( _ ) Isooxyskyanthine 183 [180].…”

Macrocyclisations using allylic radical intermediates. A new synthetic approach to natural 14-membered cembranoids

“…The mixture was stirred at room temperature for 17 h and then filtered under suction. Evaporation 26.0 (t), 25.5 (q), 21.7 (2 x q), 19.2 (q), 17.5 (9) 1 5-Hydroxy-2,6,lO,l4-tetramethyl-3-methylenepentadeca-5(E),9(E), 13(E)-trien-4-one 20a.-A solution of the trienone 19 (100 mg) in dichloromethane (1 cm3) was added in a single portion to a stirred mixture of selenium dioxide (18 mg) and tert-butyl hydroperoxide (90% solution; 0.1 cm3) in dichloromethane (4 cm3) at 0 "C.,, The stirred mixture was allowed to warm to room temperature over 2 h before it was concentrated to leave a yellow residue which was taken up immediately in diethyl ether (5 cm3). The solution was washed with aqueous sodium hydroxide (lo%, 2 x 5 cm3) and then with brine (5 cm3).…”