Enones trisubstituted

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]. 

A similar trend was observed in the reaction of tri- and tetrasubstituted etiolates derived from 2-unsubstituted or 2-bromo substituted 3,4-dihydro-6-methoxy-1(2//)-naphthalenone16. The trisubstituted cnolate underwent addition to (—)-(2 )-2-(4-methylphenylsulfinyl)-2-cyclopen-tenone via attack on the nonchelated conformation to give an adduct of d.r. [(2S)/(2/ )] 77 23. The tetrasubstituted enolate underwent addition to the corresponding ( + )-(5)-enone via attack on the chelated conformation to give an adduct with the same absolute configuration at C-2 but with d.r. [(2R) (2S)] 95.5-97 4.5-3. 

Carbon-carbon double bonds in unconjugated alkenes usually exhibit weak to moderate absorptions due to C=C stretehing in the range 1660-1640 em V Disubstituted, trisubstituted and tetrasubstituted alkenes usually absorb near 1670 cm The more polar carbon-carbon double bonds in enol ethers and enones usually absorb strongly between 1600 and 1700 crn k Alkenes conjugated with an aromatic ring absorb strongly near 1625 crn k... 

Figure 3.7. Scope of Cu/29-catalyzed asymmetric 1,4-addition of diorganozinc reagents to trisubstituted cyclic enones.

When the 4-position is substituted, Grignard addition occurs at the 2-position, to eventually give a 2,4,6-trisubstituted pyridine via the 6-lithiated species (Scheme 145) (88TL1751). Alternatively, if the 4-substituent is a chloro (88TL1751) or methoxy group (89TL5053), the initial product can be hydrolyzed to an enone rather than being aromatized to a pyridine. 

These mixed cuprates undergo conjugate addition to mono-, di-, and trisubstituted enones in good to excellent yield. Additives such as S(CH3)2 and R3P, which are sometimes necessary in Michael additions of R2CuLi, are not necessary.9... 

Hawner C, Li K, Cirriez V, Alexakis A (2008) Copper-catalyzed asymmetric conjugate addition of aryl aluminum reagents to trisubstituted enones construction of aryl-substituted quaternary centers. Angew Chem Int Ed 47 8211-8214... 

Various 1,2,4-trisubstituted pyrroles 30 have been prepared using a palladium catalyzed reaction of the enones 31 with glycine ethyl ester as outlined in the example below, or benzylamine catalyzed by Pd(PPh3)4 to give the corresponding 1-benzylpyrroles <02SL619>. 

Two related procedures employing osmium in catalytic quantities, and providing, unlike the above, a removable nitrogen substituent, have been developed. 468 Scheme 51 represents a procedure suitable for mono- and 1,2-di-substituted alkenes, but which is too vigorous for diethyl fumarate and enones Scheme 52 is suitable for 1,1-di- and tri-substituted alkenes Scheme 53 is applicable to mono- and 1,2-di-substituted alkenes, especially electron-deficient alkenes, and can be extended to trisubstituted alkenes by incorporation of EuNOAc in the reaction mixture. ... 

The orientation of the substituent gtoups in 1,2,4-oxadiazole substituted pyrazoles 39, formed by reaction of benzonittile oxides with an unsymmetrically substituted hydrazine, has been determined by C NMR assignments <1998JHC161>. The scope and limitations in the regioselective synthesis of 1,3,5-trisubstituted pyrazoles from / -amino enones and hydrazine derivatives were investigated by C chemical-shift prediction mles for 1,3,5-trisubstituted pyrazoles <2001H(55)331>. 

The protection was necessary in order to avoid the formation of the enone-type compounds during the generation of the allene intermediate. Heating 119 in the presence of potassium t-butoxide generated the allene intermediate which underwent an in situ electrocyclic cyclization to furnish the desired trisubstituted carbazole 120 after tautomerization. Triflate 121 was obtained... 

The same kind of associative event lies at the heart of the catalytic asymmetric epoxidation of enones using the interesting binaphthyl derived spiro ammonium salt 33, which serves as a phase transfer catalyst as well as chiral auxiliary. Using sodium hypochlorite in a biphasic system, this catalyst mediates the high-yielding epoxidation of a variety of electron-deficient trisubstituted and trara-disubstituted olefins with excellent enantioselectivity, as represented by the conversion of enone 34 to the corresponding epoxy ketone 35 <04JA6844>. 

The aldol reaction is often used to make enones by dehydration of the aldol itself, a reaction which often occurs under equilibrating aldol conditions, but has to be induced in a separate step when lithium enolates or silyl enol ethers are used. In general one has to accept whatever enone geometry results from the dehydration, and this is usually controlled by thermodynamics, particularly if enone formation is reversible. Simple enones such as 46 normally form as the E isomer but the Z isomer is difficult to prepare. When the double bond is exo to a ring, e.g. 47, the E isomer is again favoured, but other trisubstituted double bonds have less certain configurations. 

Most of the examples in this chapter have been disubstituted alkenes, a few have been trisubstituted, but none so far has been tetrasubstituted (except cyclic alkenes) as this is the most difficult case of all. One solution49 starts with ethyl lactate 228 and uses a HWE reaction on the enantiomerically pure phosphonate 229 to make the / -enone 230 with very high selectivity. Chelation-controlled addition of a Grignard reagent gives the stereochemically pure allylic alcohol 231. Chelation control is explained in chapter 21. 

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