3-Ethyl-2-cyclohexenone

Cyclohexenone has been prepared by dehydrohalogenation of 2-bromocyclohexanone, by the hydrolysis and oxidation of 3-chlorocyclohexene, by the dehydration of a-hydroxycyclohexa- ione, by the oxidation of cyclohexene with chromic acid or hydrogen peroxide in the presence of a vanadium catalyst, by I lie addition of acroleiti to ethyl acetoacctate followed by cycliza-lion, hydroly.sis, and decar])oxylation, by the reduction of N,N-dimelliyliiniline with sodium and ethanol itt liquid ammonia... 

Ethoxy-2-cyclohexenone has been prepared by reaction of the silver salt of dihydroresorcinol with ethyl iodide and by the reaction of dihydroresorcinol with ethyl orthoformate, ethanol and sulfuric acid." The acid-catalyzed reaction of dihydroresorcinol with ethanol in benzene solution utilized in this preparation is patterned after the procedure of Frank and Hall. ... 

At higher temperatures the mixture of 10 and methyl vinyl ketone yields the 1,4-carbocyclic compound as described previously. Methyl isopropenyl ketone (5), ethyl acetylacrylate (d), 2-cyclohexenone (21), and 1-acetyl-1-cyclohexene (22) also undergo this type of cyclization reaction with enamines at higher temperatures. This cycloalkylation reaction occurs with enamines made of strongly basic amines such as pyrrolidine, but the less reactive morpholine enamine combines with methyl vinyl ketone to give only a simple alkylated product (7). Chlorovinyl ketones yield pyrans when allowed to react with the enamines of either alicyclic ketones or aldehydes (23). 

The Robinson annulation of ethyl acetoacetate and trans-chalcone proceeded smoothly to give 6-ethoxycarbonyl-3,5-diphenyl-2-cyclohexenone in 48 % yield. The product was separated from the ionic liquid by solvent extraction with toluene. In both these reactions, the ionic liquid [HMIM][PF6] was recycled and reused with no reduction in the product yield. 

The third and fourth steps in the synthesis of Hagemann s ester from ethyl acetoacetate and formaldehyde (Problem 23.50) are an intramolecular aklol cyclization to yield a substituted cyclohexenone, and a decarboxylation reaction. Write both reactions, and show the products of each step. 

In contrast, a-alkoxycuprate 10, prepared from the corresponding stannane, gave the conjugate addition product with only 0-20% ee upon treatment with 2-cyclohexenone in the presence ofchlorotrimethylsilane67. However, the conjugate addition of 10 to ethyl propynoatc in the presence of chlorotrimethylsilane provided 11 in 85% yield with nearly 96% ee67. 

A solution of 4.5 g (19.9 mmol) 4-(fm-butyldimethylsilyloxy)-2-cyclohexenone and 452 mg (1 mmol) of mercury(II) iodide is stirred at r.t. for 15 min and then cooled to — 78 °C. 5.03 g (24.8 mmol) of 1-ethoxy-1-(tm-bulyl(iimethylsilyloxy)ethene are added dropwise during 15 min. The mixture is stirred at — 78 °C for 2 h, quenched with 302 mg (3 mmol) of triethylamine and allowed to warm to r.t. The mixture is filtered through a short (3 cm) column of silica gel (deactivated with a 5% triethylamine solution in hexane/ethyl acetate, 10 1) eluting with hexane/ethyl acetate (10 1) and concentrated in vacuo. Purification of the crude material by flash chromatography (silica gel, hcxanc/cthyl acetate 30 1) gave the adduct as a colorless oil yield 7.98 g (18.7 mmol, 94%) d.r. (cisjtrans) 95.2 4.8. 

Cyclohexene, purification of, 41, 74 reaction with zinc-copper couple and methylene iodide, 41, 73 2-CyclohEXENONE, 40,14 Cydohexylamine, reaction with ethyl formate, 41, 14... 

Reagent % yield from 2-cyclohexenone % yield from isophorone % yield from ethyl 2-butynoate (dr)... 

Fig. 7.3. a) X-ray structure of the Cul complex 21 of ligand 14 b) Possible bimetallic intermediate involved 19 in si-face-selective ethyl transfer to 2-cyclohexenone. 

Bicyclic Lactams. (S)-4-Ethyl-4-allyl-2-cyclohexenone A. I. Meyers and 0. Berney, Department of Chemistry,... 

The Robinson annulation of ethyl acetoacetate and tra i -chalcone was investigated with pulverized NaOH in [BMIMjPFg as the base catalyst at 100°C 110). The mixture was neutralized before extraction with toluene. The product, 6-ethoxycarbonyl-3,5-diphenyl-2-cyclohexenone, was obtained by purification in a silica gel chromatography column. A yield of 48% was obtained (Scheme 7). The ionic liquid could be recycled and reused with no diminution of product yield. The C2 position in imidazolium cations is an acidic proton donor and may have reacted... 

To a solution of LDA (40mmol) in THF (200ml) cooled at -45°C, methyl dithioacetate (3.92 ml, 40 mmol) was added dropwise. The yellow colour rapidly disappeared. The mixture was stirred for 5 min. 2-Cyclohexenone (3.92 ml, 40 mmol) was then added dropwise. A yellow colour appeared. The resulting mixture was stirred for 15 min. An aqueous solution of ammonium chloride was added and the mixture partitioned between ether and brine. The organic layer was washed with brine, dried with magnesium sulfate and concentrated. Methyl (cyclohexanone-3-yl)dithioacetate (3) (6.75 g, 33.4 mmol, 83%) was isolated by flash chromatography on silica gel using cyclohexane/ethyl acetate (9 1) as the eluent. 

Conjugate additions of carbamates to a, P-unsaturated enones require - apart from metal halide - TMSC1 as a stoichiometric additive [96]. The addition of ethyl carbamate to cyclohexenone (41h) requires only 50mol% TMSC1, which was an exceptionally low amount compared with other Michael acceptors. With 10 mol% of the catalyst, the yield of 3-aminocyclohexenone derivative 66 was good (93%) [97], Aza-Michael reactions also proceed in aqueous media with good results if Co(II),... 

In related studies, Mukaiyama et al. identified 2-(anilinomethyl)-l-ethyl-4-hydroxypyrrolidine 68 as a very efficient catalyst of the addition of thiophenols to cycloalkenones [54a-c]. This catalyst, which was prepared from hydroxyproline in five steps, afforded up to 88% ee in the addition of thiophenols to cyclohexenone (Scheme 4.33). 

A further example of the use of 2//-thiopyrans as surrogates for m-substituted dienes involves the use of the protected 3,4-dihydio-3-(3-oxobutyl)A//-thiopyranA-onc, 3-[2-(2-methyl-l,3-dioxolan-2-yl)ethyl]-4-[tris(l-methy-lethyl)silyl)oxy-2//-thiopyran 328 as an equivalent of l-ethenyl-2-methylcyclohexene in Diels-Alder reactions. The thiopyran reacted with various maleimides to yield the endo cycloadducts and with methyl propenoate to give the exo adduct under either thermal or Lewis-acid-catalyzed conditions. In the latter case concomitant release of the protected ketone functions occurs, acid-catalyzed cyclization of which generates a fused cyclohexenone ring (Scheme 67). Desulfurization, preferably before the aldol cyclization, leads to derivatives of 2,3,4,4a,5,6,7,8-octahy-dro-4a-methylnaphthalenes < 1997CJC681 >. 

The synthesis of ETHYL a-(BROMOMETHYL)ACRYLATE and METHYL a-(BROMOMETHYL)ACRYLATE makes these valuable intermediates readily available for the synthesis of a-methylene-y-bu-tyrolactone derivatives and other substances as well. A simple procedure for the preparation of 2-alkyl-2-cyclohexenones by reductive alkylation of o-anisic acids is demonstrated in the preparation of 2-HEPTYL-... 

Microwave irradiation of a mixture of cyclohexenones and ethyl acetoacetate adsorbed on the surface of solid lithium 5-(2)-prolinate leads to the stereoselective construction of bicyclo[2.2.2]octanone (69) systems through Michael addition and subsequent intramolecular aldolization (Ranu et al., 2000). Electron-rich aromatic compounds react with formaldehyde and a secondary amine under solvent-free condition and microwave irradiation in a microwave oven to produce amino ethylated products (70) in good to excellent yields (Mojtahedi et al., 2000). 

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