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Cyclohexenones enol ether preparation

A method of synthesis which has been used generally in this series employed a Fischer reaction at an early stage to form the tetrahydrocarbazolone nucleus [59] (Scheme 7.2). We devised a second route employing the Fischer method in which the key intermediate was the cyclohexenone (22) (Scheme 7.3). This was readily prepared by treating the enolate of the methyl enol ether (21) with dimethyl(methylene)ammonium iodide [60] to form the Mannich base which was then condensed with 2-methylimidazole to give (22). [Pg.255]

Elimination of the Pd enolate 253, formed by the transmetallation of 252, is a good synthetic method of the enones 254 [152], The silyl enol ether 255, prepared by trapping the conjugate addition product of cyclohexenone, is dehydrogenated with... [Pg.448]

Pd(OAc)2 to give the cyclohexenone 256. In clavulone synthesis, only the silyl enol ether in 257 reacts with Pd(OAc)2 to give the enone 258 [153]. The dehydrogenation can be carried out with a catalytic amount of Pd(OAc)2 using benzoquinone as the reoxidant. Cyclopentenone (260) is prepared from cyclopentanone (259) by using a supported Pd catalyst under 02 atmosphere [154], The enone 261 is converted to the dienone 263 via the dienol silyl ether 262 [155],... [Pg.449]

Formation of Cyclohexenones. Hydrolysis of the initial enol ether (vinyl ether) formed from Birch reduction of anisole or substituted anisoles under mild acidic conditions leads to P,y-unsaturated cyclohexenones. Under more drastic acidic conditions, these isomerize to the conjugated a, 3-cyclohexenones. Birch reduction of anisoles followed by hydrolytic workup is one of the best methods available for preparing substituted cyclohexenones. ... [Pg.149]

Conjugate addition. Trialkylstannyllithium reagents prepared in ether solution undergo predominantly 1,2-addition to cyclohexenones, but solutions prepared in THF undergo conjugate addition to almost all enones, even hindered ones. The intermediate lithium enolates can be alkylated with reactive alkyl halides. These reactions are useful because secondary alkylstannanes are converted into the corresponding carbonyl compound by oxidation with Cr03-2Py. Tertiary alkylstannanes are also oxidized by CrOa-lPy, but mixtures of alcohols and products of dehydration are formed. [Pg.253]

Preparation of enones from saturated ketones by Pd(II)-promoted dehydrosilyla-tion via silyl enol ethers was reported by Ito. Transmetallation of the silyl enol ether of cyclohexanone 519 with Pd(OAe)2 gives the oxo-TT-allylpalladium complex 520 (Pd enolate), which undergoes -H elimination to afford cyclohexenone. BQ is used as an oxidant of Pd(0) [211], However, the enone formation can be carried out using a catalytic amount of Pd(OAc)2 in DMSO under oxygen without other oxidants at room temperature. Also aldehyde 521 is converted to unsaturated aldehyde 522 via silyl ether in DMSO [4],... [Pg.95]

The enone formation has been applied to a number of natural product syntheses. The enone 524 was prepared from the complex molecule 523 and successfully applied to the total synthesis of pallescensin [212], Even the phenolic OH in 525 was converted to the conjugated ketone. The reaction was utilized as a key step in hypoxyxylerone synthesis [213]. In the total synthesis of galbulimima alkaloid GB 13, Mander converted a cyclohexanone in the complicated molecule 526 to the corresponding cyclohexenone via silyl enol ether in 82% yield [214]. [Pg.95]

Methyl-3-cyclohexenone was prepared by Birch reduction of p-methylanisole followed by hydrolysis of the resulting enol ether, cf. A. J. Birch, J. Chem. Soc., 596 (1946). [Pg.185]


See other pages where Cyclohexenones enol ether preparation is mentioned: [Pg.209]    [Pg.438]    [Pg.209]    [Pg.120]    [Pg.803]    [Pg.848]    [Pg.61]    [Pg.223]    [Pg.93]    [Pg.803]    [Pg.848]    [Pg.51]    [Pg.333]    [Pg.171]    [Pg.236]    [Pg.373]    [Pg.77]    [Pg.325]    [Pg.366]    [Pg.180]   
See also in sourсe #XX -- [ Pg.599 ]

See also in sourсe #XX -- [ Pg.599 ]

See also in sourсe #XX -- [ Pg.599 ]




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2-Cyclohexenone

Cyclohexenones

Cyclohexenones preparation

Enolate preparation

Enolates preparation

Enols preparation

Ethere preparation

Ethers preparation

Preparing Ethers

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