Ap-Unsaturated carbonyl compounds

Ballini, R., Marotta, E., Petrini, M., and Rosini, G. 1986. Conjugate addition of nitro derivatives to aP-unsaturated carbonyl compounds on basic alumina. Synthesis, 3 237-8. 

Further details have appeared of the condensation of the dimethylsulphoxonium ylide (23 R = H or Me) with aP-unsaturated carbonyl compounds, which were discussed in an earlier Report. In the attempted alkylation of the ylide (24) with phenacyl bromide the ylide functions solely as a base, trans-l,2,3-tribenzoylcyclo-propane being the sole product formed in high yield. ... 

General Preparations.—Alkenes. Dehalogenation of vicinal dihalides is easily carried out using sodium in liquid ammonia, e.g. 1,2-dichlorocyclo-octane gave ds-cyclo-octene in 95% yield.The scope of the synthesis of ap-unsaturated carbonyl compounds by syn-elimination from 2-phenylselenoxides has been studied only low yields of the desired ketone were obtained from 2-phenylseleno-cycloheptanone and cyclo-octanone because of the competing Pummerer rearrangements, but improved yields could be obtained by prior conversion of the ketones into ketals. The reaction worked well for 2-methoxycarbonyl cyclic ketones, e.g. 2-methoxycarbonylcyclo-oct-2-en-l-one was prepared in 93% yield. ... 

Apart from routine applications to cyclopropane synthesis,the application of new catalysts to the decomposition of diazo-compounds has received considerable attention. The use of palladium acetate, originally reported in 1972 by Paulissen et o/., has been extended and applied to diazomethane and ethyl diazoacetate in the presence of aP-unsaturated carbonyl compounds. With a- and a-substituted aP-unsaturated ketones, stereospecific cis-addition occurs in excellent yields, but the catalyst proves to be ineffective with analogous trisubstituted olefins, as illustrated for the formation of (110) with diazomethane. The use of palladium chloride with the... 

Condensatitm Reactions.—Additions of dimethylsulphonium and dimethyl-sulphoxonium methylides to ap-unsaturated carbonyl compounds continue to be good routine methods of preparing cyclopropyl derivatives. ... 

Fluoroalkenes have also been condensed with ynamines and fluoroallenes with thiols, and two groups have reported the reactions of ynamines with P-unsaturated carbonyl compounds. Here, the initial product may undergo a doublebond shift to give the conjugated P-amino-aP-unsaturated carbonyl derivative. An example of the synthetic utility of this reaction is shown in Scheme 22. 

Spectra.—For compounds of low solubility in deuteriochloroform, the use of ASCI3-CDCI3 (2 1 v/v) may prove valuable as the chemical shift differences (excepting alcohols) between the two solvent systems is negligible (< 1 p.p.m.) on the n.m.r. scale. Titanium tetrachloride-induced shifts on the spectra of carbonyl compounds has been investigated. The carbonyl carbon atoms experience large down-field shifts, adjacent carbon atoms showed only small downfield shifts, and remote carbon atoms are scarcely perturbed. In a -unsaturated carbonyl compounds, large downfield shifts are observed for the P-carbon atoms, presumably because of the enhancement of the dipolar resonance form of the enone system consistent with this picture is the much smaller shift, in either direction, of the a-carbon atoms. Studies were extended to include ap-unsaturated acids and esters. ... 

The Wittig reaction can oifer a powerful alternative to the aldol reaction for construction of a -unsaturated carbonyl compounds. (2,2-Diethoxyethylidene)-triphenylphosphorane shows very high stereoselectivity in reactions with aldehydes to give (Z)-ap-unsaturated aldehyde acetals, which may readily be cleaved to the less stable (Z)-isomer of the enal [equation (21)]. Alkenyl fluoromethyl... 

Compounds containing a double or triple bond, usually activated by additional unsaturation (carbonyl, cyano, nitro, phenyl, etc.) In the ap position, add to the I 4-positions of a conjugated (buta-1 3-diene) system with the formation of a ax-membered ring. The ethylenic or acetylenic compound is known as the dieTwphile and the second reactant as the diene the product is the adduct. The addition is generally termed the Diels-Alder reaction or the diene synthesis. The product in the case of an ethylenic dienophile is a cyctohexene and in that of an acetylenic dienophile is a cyctohexa-1 4-diene. The active unsaturated portion of the dienophile, or that of the diene, or those in both, may be involved in rings the adduct is then polycyclic. 

The bicyclo[2,2,l]heptane system also continues to find employment for the assessment of new synthetic procedures, or for testing the efficacy of new reagents. Isolated yields of 50—65 % of ap-unsaturated aldehydes have been obtained by reaction of alkyl tosylhydrazones with butyl-lithium, addition of DMF, and hydrolysis however, reaction of camphor tosylhydrazone (381 X = NNHTs) according to this procedure only gave 10 % of the aldehyde (382 X = CHO), presumably because of unfavourable steric effects. " Trimethylsilyl trifluoromethanesulphonate is a mild reagent for converting carbonyl compounds into trimethylsilyl enol ethers, for example the production of (382 X = OSiMcj) from camphor (381 X = Experimental details... 

Other Unsaturated Alcohols. An improved procedure that has been reported recently for the preparation and utilization of alkali-metal acetylides in liquid ammonia allows the ethynation of sensitive carbonyl compounds to be carried out, in good yield, to give propargylic alcohols. The reduction of ap-acetylenic ketones to (S propargyl alcohols of high enantiomeric purity can be performed with NB-Enantrane (27) [cf. (6) earlier], which is derived from nopol benzyl ether as a low-cost alternative to (—)-a-pinene. a-Allenic alcohols have been prepared by the new routes shown in Schemes... 

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