Enones alicyclic

Polycyclic oxetanes are obtained in good yields in intramolecular carbonyl-olefin cycloadditions, in an analogous way as the corresponding alicyclic systems are formed in intramolecular enone-olefin additions. Two applications are given in (4.78)492) and in (4.79)493). 

Various groups have reported that additions of a-hetero substituted ester enolates to a,3-enones are temperature dependent, l40 c but, in general, the 1,2 to 1,4-equilibration of a-seleno and a-thio substituted ester adducts occurs at lower temperature than the a-oxo substituted ester adducts. In contrast to the simple ester enolates, the a-hetero substituted ester enolates are extremely useful for functionalization of alicyclic a,(3-enones with the tandem conjugate addition-electrophile trapping protocol, as shown... 

Alicyclic enol acetates can lead to the corresponding enones by anodic oxidation. The electrolysis of d-menthenyl acetate 74 in an AcOH—Et4NOTs—(C) system by passing 2.5 F/mol of electricity provides the d-menthenone 75, a precursor for d-menthone 76 and /-citronellol 54 syntheses, in 97% yield (Scheme 3-28)76a). 

The alicyclic ketones have been identified as being important flavor precursors by Flament et al. (15) and more recently by MacLeod and Ames (44), who identified a similar compound (3-methyl-cyclo-pentanone) in heated ground beef. Flament et al. (15) singled out the importance of these compounds, particularly in the presence of alhylpyrazines. Nishimura et al. (41) produced a meaty odor by heating 2-hydroxy-3-methylcyclopent-2-enone with cyclotene and HaS. Two volatile compounds described as having meaty odor were 2-methyl-cyclopentanone and 3-methylcyclopentanone. Thus, cyclotene appears to be a key precursor of "roast beef" flavor. 

Reduction of enol ethers or enol esters of 1,3-diketones, followed by acid-catalyzed allylic rearrangement of the reduction product (see p. 85 in ref. 5) is a useful route to a,P-unsaturated ketones. Ali-phatic - and alicyclic enones have thus been prepared in good yields at low temperatures with NaAlH2(0CH2CH20Me)2.2 6... 

The ring contraction rearrangement of alicyclic a-diketones is much more valuable from the synthetic viewpoint e.g. equation 4). There are several routes available for the synthesis of a-diketones from monoketones. These include direct oxidation using selenium dioxide permanganate or osmium tetrox-ide addition across the double bond of an enone followed by base-promoted elimination of water bromi-nation to give the dibromo ketone followed by hydrolysis condensation with 4-nitroso-/V,/V-dimethylaniline followed by acidic hydrolysis — but there are many others. The bromination-hydrolysis route has been extensively studied by Wallach." The conversion of menthone into 1-hydroxy-... 

Tetrahydroxanthen-l-ones are obtained from the reaction of salicyl Af-tosylimines with alicyclic enones. Ring size controls the amounts of the Baylis-Hilhnan adduct which are also isolated <05SL2623>. 

The products (4) derived from alicyclic ketones are useful for synthesis of spiro compounds. For example, the product (5) obtained from cyclohexanone has been transformed in several steps into the spiro enone (6) and into the spiro diketone (7). 

The nucleophilic intermediate obtained by treatment of enones with MejCuLi in diethyl ether at 273 K under nitrogen has been rnade to give aldol condensation products with zinc chloride and excess acetaldehyde. Thus cyclohexenone gave 97 % of (34), which on dehydration gave the enone (35) in 87 % yield. Introduction of an isoprene function onto an alicyclic system has been accomplished " via the reagent (36) with saturated and unsaturated alkanones at low temperatures (195 K). 

The first report of the reaction of 2//-l-benzopyran (139) with various 1,3-dipoles has appeared/ Good yields of single cycloaddition products (140) were obtained upon reaction with nitrile-imines, whereas nitrile oxides gave 1 1 mixtures of the regioisomers (141) and (142), The reactions with diazomethane gave rather inconclusive results, and phenyl azide and diphenyl nitrone failed to react. Similar types of reactions have been carried out using a variety of enones in which the overall conclusion appears to be that simple aliphatic or alicyclic enones produce mixtures of regioisomers upon reaction with nitrile oxides and nitrile imines whereas enones of the chalcone type show only one product. Experts in FMO theory will probably declare these results... 

Dicarbonyl Compounds.—Ozonolysis of 2-cyclopentylidenecyclopentanone provides a convenient synthesis of cyclopentane-l,2-dione on the ca. 0.4 mole scale.The by-product, cyclopentanone, is recycled via an aldol condensation to regenerate the enone. The method should be applicable to other alicyclic 1,2-diones. Various methods for the preparation of monoprotected 1,2-diones have appeared. Monoacetals of a-dicarbonyl compounds are prepared regio-specifically from enol ethers [equation (32)], following epoxidation in methanol and oxidation of the resulting acyloin acetal. 

Sussangkarn, K. Fodor, G. Karle, I. George, C. (1988) Ascorbic acid as a Michael donor. Reaction with alicyclic enones. Tetrahedron, 44,7047-54. 

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