Y,S-Unsaturated ketones

The intramolecular equivalent of the Paterno-Biichi reaction has been observed in a number of unsaturated ketones. A series of y,S-unsaturated ketones (278) are converted in this way into the oxabicyclo[2.2.0]hexanes (279) and the oxabicyclo[2.1.1]hexanes (280), both photoproducts being the result of 1,2-cycloaddition.303... 

Intramolecular cycloaddition, particularly in y,unsaturated ketones,348 has also been reported. Recent examples include the photochemically induced conversion of the cyclohexanone (397) to the two possible adducts (398 and 399)349 ancj the formation of the oxetans (400) from 5-acylnorbomenes (401 ).350 The introduction of an ether oxygen into the unsaturated ketone... 

Saucy, G., Marbet, R. Reaction of tertiary vinylcarbinols with isopropenyl ether. New method for the preparation of Y,S-unsaturated ketones. Helv. Chim. Acta 1967, 50, 2091-2094. 

Synthesis of y,8-unsaturated ketones.3 Isopropenyl methyl ether reacts with tertiary vinylcarbinols to give y,S-unsaturated ketones. Phosphoric acid is used as... 

The addition of 2 moles of the Grignard reagent, R MgBr, to a-chloro acid chlorides, R R C(Cl)COCl results in the formation of alkenes R R C=CR 2 >n creditable yields, and excellent yields of Y,S-unsaturated ketones are obtained by the addition of vinylmagnesium bromide to imidoyl chlorides. Finally, unsymmetrical alcohols, R R CHOH are prepared in a convenient one-pot procedure by the stepwise addition of R MgX and R MgX to 2(iV-formyl-iV-methylamino)pyridine. ... 

Among the applications of allyl silanes reported this year their reaction with phenylselenyl chloride and subsequent oxidation of the resulting allyl selenides to allylic alcoholshas been used in the sequence outlined in Scheme IS. 3-Bromoallyltrimethylsilane therefore behaves as a hydroxypropenyl synthon. Nitroalkenes react with allylsilanes to give, after hydrolysis, y,S-unsaturated ketones, and a synthesis of substituted cyclopentenones based on this procedure has been described.Allyl trimethylsilyl ethers undergo a palladium-promoted coupling with aryl iodides to give /3-aryl-a,/3-unsaturated ketones, and palladium also catalyses the reaction of various aryl bromides with trimethylsilyl acetylene to produce ethynylated aromatics. 

A similar rearrangement takes place with allyl vinyl ethers, leading to a so-called y,S-unsaturated ketone or aldehyde. 

Scheme J.S5 Divergent synthesis of isomers ( or Z) of protected y,S-unsaturated ketones by the Horner-Wittig reaction.

Hydroboration. y,S-Unsaturated ketones can be synthesized in good yield from methyl vinyl ketone and 9-borabicyclo[3,3,l]nonane as illustrated in Scheme 39. The coupling of hydrobated olefins with silver ions has been extended to dienes. 

Cuprous methyltrialkylborates (54), which are prepared from trialkylboranes, methyl lithium and cuprous halide, are useful alkylating agents. Reaction with acrylonitrile for example gave the corresponding 1,4-adducts which are converted into alkyl cyanides by hydrolysis (Scheme 6). Yields are generally excellent, provided cuprous bromide is used and not the chloride or iodide. The complex (54) also reacts readily with 1-acyl-2-vinylcyclopropane to form 1,6-adducts which are hydrolysed to the corresponding /raws -y.S-unsaturated ketone (55) in good yield. 

CLAISEN - IRELAND Rearrangment Rearrangement ol allyl phenyl ethers to o (or p-)allylphenols or of allyl vinyl ethers to y.S-unsaturated aldehydes or ketones (Claisen) Rearrangement ol allyl esters as enolale anions to y.S-unsaturated acids (Ireland)... 

Treatment of a-(benzotriazol-l-yl)alkyl thioethers 831 with ZnBr2 weakens the bond with benzotriazole, and the obtained complex 832 may partially dissociate to thionium cation 835 that can be trapped by even mild nucleophiles. Thus, trimethylsilyl cyanide added to the reaction mixture causes substitution of the benzotriazole moiety by the CN group to give a-(phenylthio)carbonitrile 834. In a similar manner, treatment with allylsilane leads to y,S-unsaturated thioether 833. Addition of species 835 to the double bond of a trimethylsilyl ot-arylvinyl ether followed by hydrolysis of the silyloxy group furnishes (i-(phenylthio)alkyl aryl ketones 836 (Scheme 132) <1996TL6631>. 

RuCp(COD)Cl-catalyzed addition of allyl alcohol to alkynes to form y,d-unsaturated ketones was developed by Trost at al. [37] in DMF-H20. Different from Trost s catalyst, Derien et al. [38] used [RuCl(C5Me5)]4, RuCl2(methal-lyl)(C5Me5) and RuCl(COD)(C5Me5) as catalysts to regioselectively form y,S-unsaturated aldehydes in aqueous media with the branched aldehydes as the major products (Eq. 19). 

Most recently, B-halo-l-alkenyl-9-BBN s have revealed to undergo a 1,4-addition reaction to ae,P-unsaturated ketones such as methyl vinyl ketone. Hydrolysis of the initially formed intermediates produces the corresponding (Z)-5-halo-y,5-unsaturated ketones in good yields stereospecifically (>98%),88). In the reaction with methyl vinyl ketone, the major products isolated after hydrolysis are not the expected halo-enones but the aldol adducts, which are readily converted into the halo-enones by treatment with sodium hydroxide, as depicted in Scheme 3. No aldol adducts are formed in the case of enones other than methyl vinyl ketone. 

Metal catalyzed cross-coupling reactions with acylzirconocene chlorides and various organic halides or acetates can give rise to unsymmetrical ketones or a mixture of /3,y-and a ,/3-unsaturated ketones (Scheme 22). The advantage of the use of a Cu catalyst instead of a Pd catalyst is to avoid the undesirable formation of a ,/S-unsaturated ketone. ... 

Cyclopentanones. Exposure of y,S-unsaturated aldehydes to 1 equiv. of stannic chloride in CH2CI2 at 0° furnishes cyclopentanones. Cyclization of the (E)-aldehyde 1 thus produces the cyclopentanone 2, whereas the corresponding (Z)-aldchyde 3 cyclizes to ketone 4. ... 

Cyclic a -nucleofuge-a,)S-unsaturated ketones 35 (X = Cl, Br, OMs) similarly condensed with dimethyl sodiomalonate but the yields of cyclopropanols were poorer (14-20%). The cyclopropanols 36 were obtained as mixtures of diastereomers, which were accompanied by bicyclic y-lactones 37 in 15-22% yield. ° ... 

Vinyl aluminium compounds also carry out conjugate additions and illustrate well the difference in reactivity between vinyl alanes and the related ate complexes. If the enone can adopt the s-cis conformation, as in 175, a cyclic mechanism is possible in which aluminium both acts as a Lewis acid and delivers the vinyl nucleophile. Notice that the Zs-vinyl alane leads to the -y,8-unsaturated ketone 178 as this is again an SE2 reaction at the vinyl carbon.32... 

Colchicide (XXII) appears to have a single Cotton effect, but two overlapping effects are considered more probable. Hexahydrocolchicine (a cinnamylamine with skewed chromophore) exhibits a strong negative Cotton effect at 250 mp. The j8- and y-lumicolchicines (XXIII) are essentially arylcyclobutenes combined with a, S-unsaturated ketone... 

Conjugate additions. The reagent undergoes conjugate addition to a,fi-unsaturated ketones to form y,S-acetylenic ketones. ... 

As illustrated in eq 5, a./S-unsaturated ketones undergo a,a-dialkylation when treated with excess r-BuOK/f-BuOH and an alkylating agent4 The K.a-dimethylated, y-unsaturated ketone is formed by conversion of the initially produced a-methylated /3,y-unsaturated ketone to its dienolate, which undergoes a second methylation faster than the 8, /-double bond is isomerized to the a,/3-position. ... 

Diketones were obtained mainly by the oxidation of y,8-unsaturated ketones and used for cyclopentenone anellation. 28 q, example is shown below (equation 17). However, the following y,8-unsaturated lactone was oxidized regioselectively to give l,S-ketolactone in 73% yield in one week (equation 18). ... 

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