Ketones, monocyclic

Myrcene with its conjugated diene system readily undergoes Diels-Alder reactions with a number of dienophiles. For example, reaction with 3-meth.5i-3-pentene-2-one with a catalytic amount of AlCl gives an intermediate monocyclic ketone, which when cyclized with 85% phosphoric acid produces the bicycHc ketone known as Iso E Super [54464-57-2] (49). The product is useful in providing sandalwood-like and cedarwood-like fragrance ingredients (91). 

The relation of rates of reduction with NaBH4 to variations in structure in a wide variety of monocyclic and bridged bicyclic compounds has also been discussed for example, a methyl a to a ketone slows the rate of reduction. Brown ° stated that reactions should not be discussed in terms of axial and equatorial attack, since the rates simply reflect differences in the energies of the possible transition states and not enough is known about the transition state to analyze it. He accepted th concepts of SAC and PDC, but preferred to call them steric strain contrpl and product stability control. ... 

The transformations are not sensitive to the presence of oxygen or changes in the solvent (isopropanol, ethanol, dioxane, benzene, 1,3-pentadiene). Results from studies with aliphatic and monocyclic epoxy ketones ... 

Within monocyclic ketones, a similar inversion of the migratory preference was only reported for the biooxidation of terpenones with CHMOAdneto- while (—)-dihydrocarvone is converted to the expected normal lactone, migration of the less substituted carbon center was observed for the biooxidation of antipodal (+)-dihydrocarvone, ultimately providing the abnormal lactone [185]. 

Therefore, acyclic and monocyclic nitroso acetals are convenient precursors of functionalized p-hydroxy ketones and y-aniino alcohols (see Reference 403). 

Conformational studies on monocyclic Cg to Cn ketones have been reviewed with reference to the MM method (184 see also ref. 89). Extensive comparisons of the conformational energies of trans-... 

A series of bicyclo[3.3.0]octanols are accessible by electroreductive tandem cyclization of linear allyl pentenyl ketones 189, as shown by Kariv-Miller et al. [189]. The electrolyses are carried out with an Hg-pool cathode and a Pt-flag anode. As electrolyte, tetrabutylammonium tetrafluororborate is used. The reaction is stereoselective, yielding only two isomers 192 and 193. In a competing reaction, a small amount of the monocyclic alcohol is formed. Since all the monocycles have the 1-allyl and the 2-methyl group in trans geometry it is assumed that this terminates the reaction. The formation of a bicyclic product requires that the first cyclization provides the cis radical anion which leads to cis-ring juncture [190] (Scheme 37). 

However, 2,3-dihydro-4(lH)-pyridone [248] is also claimed to be N-protonated (Sugiyama et al., 1969) because the absorption maximum of its hydrochloride occurs virtually at the same wavelength (325 nm) as for the base itself (327 nm). According to Table 5, this would be an indication of O-protonation. Monocyclic ketones ([249], R = MeCO) with uninhibited mesomerism show O-proto-... 

Although genetic studies have identified a number of putative aromatic PK aromatases and/or cyclases, in vitro characterization of these enzymes is usually difficult since the postulated Hnear or monocyclic poly 3-ketone templates are often unstable to be isolated or synthesized. For these reasons, the generality and synthetic applications of these enzymes have not been studied in most cases. However, there is plenty of evidence to suggest that enzymatic aromatization and cyclization take place for a variety of linear precursors with various chain lengths [32]. 

Acyl substituents at the 3- and/or 4-positions result in decreased hydrolytic stability compared with the alkyl and aryl derivatives described above. Despite this constraint most of the usual reactions of the carbonyl group are possible. Aldehydes <9ILA1211> and ketones are oxidized to the carboxylic acid, borohydride reduction affords the expected alcohols, and epoxides are formed on reaction with diazomethane. Oximes and arylhydrazones are formed with hydroxylamine and arylhydrazines, and the products may subsequently undergo monocyclic rearrangement involving the oxadiazole to give the corresponding isomeric furazans and 1,2,3-triazoles (Section 4.05.5.1.4). 

A highly versatile method for the synthesis of a variety of 6-membered monocyclic and fused bicyclic peroxylactols 440 from activated ketones 438 (EWG = electron-withdrawing... 

Reactions of this type provide major routes to both the monocyclic system and to 1,5-benzothiazepines. In some cases the reactions are single-stage processes but in many cases the intermediate produced by the primary formation of the S—C bond can be isolated. Thus 2-aminoethanethiol reacts with a,/3-unsaturated or j3-halogeno ketones to give (408). Similarly reaction with a,/3-unsaturated acids, esters or acid chlorides and with 3-halogenopropionyl halides gives the 5-oxo derivative (409). 2-Aminoethanethiol also reacts with activated 2-chlorobenzophenones to give 1,4-benzothiazepines. 

As with 1,4-oxazepines the Schmidt reaction of cyclic ketones and the Beckmann rearrangement of their oximes can be applied to the synthesis of monocyclic 1,4-thiazepines, 1,4- and 1,5-benzothiazepines and their 1-oxides and 1,1-dioxides (75CJC276). 

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