Acylation of alkenes generated in situ by hydride transfer from isoalkanes. Synthesis of pentalenones, hydrindenones, and cyclopentenones
摘要:
Acylation, in the presence of AlCl3 and hydride acceptor, of methylcyclopentane, methylcyclohexane, and 2-methylbutane by ethylenic acyl chlorides, in CH2Cl2 solution, respectively, leads to tetrahydropentalenones, tetrahydroindenones, and cyclopentenones in good yields. Hydride acceptor may be either acetyl chloride or the alkenoyl chloride itself. Better results are performed in the presence of nitromethane and CuSO4. Overall yields are better than those obtained by the two-step process involving acylation of alkenes by alkenoyl chlorides and subsequent Nazarov cyclization of the resulting divinylketones. Methyl 1,4-migration is observed during the acylation of 2-methylbutane by sorboyl chloride. The mechanism of these conversions is discussed on the basis of results observed with cyclohexane-d12 and methylbutane-d6 as well as stereochemical studies of the cyclization process.
Enone construction: A silver‐mediated olefin acylation reaction is described, in which five‐, six‐, and ‐seven‐membered rings, tetrasubstituted olefins, bridged bicycles, spirocycles, and benzoxepinones are prepared. Highly selective intermolecular reactions are coupled to a Nazarov cyclization for the effective preparation of cyclopentenones, including the core of modhephene (see scheme).
A Short and Efficient Synthesis of (±)-Modhephene by a Stereoelectronically-Controlled Ene-Reaction
作者:Wolfgang Oppolzer、Kurt Bättig
DOI:10.1002/hlca.19810640756
日期:1981.11.4
(±)-Modhephene (6) has been synthesized from the easily available trimethylpentalenone 1 in 6 steps in 26% overall yield (Scheme 2). The remarkably smooth 1,4-addition/enolate trapping 1 2 and subsequent selenoxide elimination after oxidation furnished the key intermediate 3 which underwent an expedient and highly stereoselctive intramolecular ene-reaction to give the propellane 4, readily convertible
Intramolecular radical cyclization of silylacetylenic or olefinic α-iodo ketones: Application to the total synthesis of (±)-modhephene
作者:Sha Chin-Kang、Jean Tsong-Shin、Wang Deh-Chi
DOI:10.1016/s0040-4039(00)97460-4
日期:——
Silylacetylenic or olefinic α-iodo ketones were treated with tributyltin hydride and AIBN to give bicyclic ketones by an intramolecular α-carbonyl radicalcyclization reaction. As an application of this radicalcyclization reaction, the total synthesis of (±)-modhephene has been accomplished efficiently.
Vinylsilane mediated regiospecific cyclopentenone annulation of ketones
作者:William E. Fristad、David S. Dime、Bailey Thomas R、Paquette Leo A
DOI:10.1016/s0040-4039(01)86247-x
日期:1979.1
The development of a new cyclopentenoneannulation sequence of general scope which involves Friedel-Crafts acylation of a vinylsilane with an α,β-unsaturated acid chloride followed by Nazarov cyclization is reported.
A new formal total synthesis of (±)-modhephene (1) employing a chelation-controlled regioselective epoxide-carbonylrearrangement as the key step is described.