Potassium unsaturated carbonyl compounds

Triethylammonium formate is another reducing agent for q, /3-unsaturated carbonyl compounds. Pd on carbon is better catalyst than Pd-phosphine complex, and citral (49) is reduced to citronellal (50) smoothly[55]. However, the trisubstituted butenolide 60 is reduced to the saturated lactone with potassium formate using Pd(OAc)2. Triethylammonium formate is not effective. Enones are also reduced with potassium formate[56]. Sodium hypophosphite (61) is used for the reduction of double bonds catalyzed by Pd on charcoal[57]. 

Reduction of unsaturated carbonyl compounds to the saturated carbonyl is achieved readily and in high yield. Over palladium the reduction will come to a near halt except under vigorous conditions (73). If an aryl carbonyl compound, or a vinylogous aryl carbonyl, such as in cinnamaldehyde is employed, some reduction of the carbonyl may occur as well. Carbonyl reduction can be diminished or stopped completely by addition of small amounts of potassium acetate (i5) to palladium catalysts. Other effective inhibitors are ferrous salts, such asferroussulfate, at a level of about one atom of iron per atom of palladium. The ferrous salt can be simply added to the hydrogenation solution (94). Homogeneous catalysts are not very effective in hydrogenation of unsaturated aldehydes because of the tendencies of these catalysts to promote decarbonylation. 

To mention a few synthetic appHcations of trialkylsilanols, trimethylsilanol 4 adds readily to 2-chloroacrylonitrile in diethyl ether in the presence of triethylamine as triethylammonium trimethylsilanolate followed by ehmination of triethylamine hydrochloride to give 99 [32] (cf. discussion of the strongly nucleophihc properties of ammonium trimethylsilanolate 155 in Section 4.2.1). The stable potassium trimethylsilanolate 97 has also been used for the saponification of esters (Section 4.7). Dimethylphenylsilanol 100 adds readily to a,y9-unsaturated carbonyl compounds such as methyl vinyl ketone 764 in the presence of Pd(OAc)2 in a Heck-Suzuki-type reaction to give the sihcon-free /9-phenylmethylvinylketone 101 [33]. 

The potassium cyanide complex of 18-crown-6 in benzene or acetonitrile undergoes Michael addition to unsaturated carbonyl compounds (Liotta et al., 1977). In the presence of acetone cyanohydrin, the catalytic (i.e. catalytic in potassium cyanide and crown ether) cycle for hydrocyanation shown in (21)... 

The same authors (77) also investigated the Michael addition of nitromethane to a,/l-unsaturated carbonyl compounds such as methyl crotonate, 3-buten-2-one, 2-cyclohexen-l-one, and crotonaldehyde in the presence of various solid base catalysts (alumina-supported potassium fluoride and hydroxide, alkaline earth metal oxides, and lanthanum oxide). The reactions were carried out at 273 or 323 K the results show that SrO, BaO, and La203 exhibited practically no activity for any Michael additions, whereas MgO and CaO exhibited no activity for the reaction of methyl crotonate and 3-buten-2-one, but low activities for 2-cyclohexen-l-one and crotonaldehyde. The most active catalysts were KF/alumina and KOH/alumina for all of the Michael additions tested. 

Isoxazoles have been used to transpose functionality within a,/3-unsaturated carbonyl compounds (72JA9128). Thus, on exposing either (E)- or (Z)-/3-ionone oxime (449) to a mixture of iodine-potassium iodide in hot aqueous THF containing sodium bicarbonate, the isoxazole (450) was formed in high yield. Catalytic reduction of this isoxazole led... 

Methylmagnesium N-cyclohexyliso-propylamide, 189 By oxidation at an allylic carbon Selenium dioxide, 272 By reduction of a,0-unsaturated carbonyl compounds Sodium borohydride, 278 Sodium dithionite, 281 Other methods r-Butyllithium, 58 Butyllithium-Potassium f-butoxide,... 

Potassium ruthenate, 259 Dienals (see Unsaturated carbonyl compounds)... 

Phosphomolybdic acid-Potassium di-chromate-Copper(II) sulfate, 248 Tin(II) trifluoromethanesulfonate, 301 Other unsaturated carbonyl compounds Lead tetraacetate, 155 Pyrylium perchlorate, 263 Zinc-copper couple, 348 a-Substituted-a, p-unsaturated carbonyl compounds... 

Oxaspiropentanes have been obtained from the cyclopropylide 103, prepared by treatment of cyclopropyldiphenylsulfonium tetrafluoroborate 102 either with sodium methylsulfmyl carbanion in dimethoxyethane at —45 °C or with potassium hydroxide in dimethylsulfoxide at 25 °C. While the reaction of the ylide 103 with a,p-unsaturated carbonyl compounds has resulted in selective cyclopropylidene transfer to the a, 3-carbon-carbon double bond leading to spiropentanes, condensation of 103 with non-conjugated aldehydes and ketones led to oxaspiropentanes such as 104, which have been isolated in 59-100% yields, Eq. (30) 57). 

The nucleophilic cleavage of aryl alkyl ethers gives the corresponding phenol with only 1 equiv. of thiophenol in the presence of N-methyl-2-pyrrolidinone (NMP) in a catalytic amount of potassium carbonate. The aromatic nitro and chloro substituents which are displaced with stoichiometric thiolates are preserved by this method. Moreover, a(B-unsaturated carbonyl compounds do not undergo Michael addition of thiolate under these conditions. 

Addition reactions. a,0-Unsaturated carbonyl compounds 1 and 3 undergo exclusive 1,4-addition reactions with organolithium (and organomagnesium) compounds owing to steric hindrance of the carbonyl group. The adducts 2 and 4 are converted into carboxylic acids by cleavage with potassium t-butoxide and H2O in the case of 2 see potassium r-hutoxidc, this volume) and by treatment with ethanolic... 

In recent years, many chiral catalysts for the enantioselective synthesis of optical active 1,5-dicarbonyl compounds have been developed, such as chiral crown ethers with potassium salt bases and chiral palladium complexes, including bimetallic systems. Nakajima and coworkers reported on enantioselective Michael reactions of S-keto esters to a,/3-unsaturated carbonyl compounds in the presence of a chiral biquinoline N,N dioxide-scandium complex, which catalyzed the additions in high yields and with enan-tioselectivities up to 84% ee . Kobayashi and coworkers found that the combination of Sc(OTf)3 with the chiral bipyridine ligand 149 (equation 41) was also effective as a chiral catalyst for asymmetric Michael additions of 1,3-dicarbonyl compounds 147 to a,/3-unsaturated ketones 148. The corresponding Michael adducts 150 were obtained in good to high yields with excellent enantiomeric excesses in most cases (Table 10). 

A lot of progress in this area is due to the work of Trost, who introduced diphenylsulphonium cyclopropylide and phenylthiocyclopropyl lithium as extremely versatile C3-building blocks. The first reagent is easily available from the corresponding sulphonium salt by deprotonation with suitable bases (either under irreversible conditions with dimsyl sodium, or, preferably, in a reversible manner by employing potassium hydroxide in DMSO). The ylide adds to a,) -unsaturated carbonyl compounds forming... 

The formation of the C-3 adduct relies on the fact that the a,P-unsaturated alcoholate, produced, as mentioned above, by attack of the organometallic at the a-site of the a,p-unsaturated carbonyl compound, can rearrange to the enolate resulting from C-3 attack. This isomerization has been more conveniently achieved by raising the temperature to 20 C (Scheme 153, compare d to b Scheme 154 compare c to b)." It has also been performed by adding Hhff A" to the medium (Scheme 152, g Schemes 153 and 154). Otherwise, the C-3 adduct can be obtained directly, and even at -78 C, by using potassium... 

Lithium and potassium tri-sec-butylborohydride (L- and K-Selectride) selectively reduce the olefin of many a,g-unsaturated carbonyl compounds.79 The intermediate enolate anions may also be trapped by electrophiles, providing a regiospecific reductive alkylation of a,g-unsaturated carbonyl compounds. 

Alkyl trimethylsilyl ketene acetals form the expected cyclopropanes 1, using bromoform/ potassium A-rt-butoxide, in high yield. They are transformed into a-bromo-a,j8-unsaturated carbonyl compounds 2. °... 

Potassium fluoride in a two-phase system was also efficient when 18-crown-6 was present as a phase-transfer catalyst. The desilylation by fluoride produced a 7-0x0 enolate which could be reacted with various electrophiles. Appropriately substituted bicyclo[3.1.0]hexane derivatives 42 and 44 have been used to study this reaction.a,/l-Unsaturated carbonyl compounds gave rise to the formation of Michael adducts, while treatment with triphenylvinylphos-phonium salts gave bicyclo[3.3.0]octenes 46 as the result of a subsequent intramolecular Wittig reaction. 

The reaction of enol trimethylsilyl ethers of carbonyl compounds with (a,a-dihydroperfluoroalkyl) phenyliodonium triflates required promotion by potassium fluoride to proceed at room temperature to give the P-perfluoroalkyl carbonyl compounds in good yields.225 in the case of the silyl enol ether of an a,p-unsaturated ketone (119), the 6-perfluoroalkyl-o,p-unsaturated carbonyl compound (120) was the only product formed. The reaction is likely to follow a path similar to the one used in the reaction of silyl enol ethers with (perfluoroalkyl)phenyliodonium salts. In a first step, a ic-complex is formed which evolves into the cationic product of a- or y-addition, followed by desilylation to the carbonyl reaction product. 

---