Ketones a, p-unsaturated

C02Et Br KOf-Bu/THF/-20°C aliphatic and aromatic aldehydes aliphatic, cycloaliphatic and aromatic ketone, a,p-unsaturated aldehydes and ketones 52-90... 

Aryl aldehydes or ketones, a, P-unsaturated aldehydes or ketones... 

PS Wang resin 10 mol % RuH2(PPh3)4 Aldehydes, ketones, a,p-unsaturated nitriles, aldehydes, ketones, esters. [449]... 

MeaSiSCHjCHzSSiMej, Znh, EtjO, 0-25°C, 12-24h, high yields. Less hindered ketones can be selectively protected in the presence of more hindered ketones. a,P-Unsaturated ketones are selectively protected (94 1, 94 4) in the presence of saturated ketones by this reagent. ... 

HSCH2CH2SH, Zn(OTf)2 or Mg(OTf)2, CICH2CH2CI, heat, 16h, 85-99% yield. Excellent selectivity can be achieved between a hindered and an unhindered ketone. a,p -Unsaturated ketones such as carvone are not cleanly converted to ketals because of Michael addition of the thiol. ... 

With respect to the substrate scope, ketones are the most efficient nucleophiles although the intermolecular reaction works also well for esters, amides and Weinreb amides (Fig. 2.7). Regarding the Michael acceptor, enones are the best electrophiles with a wide range of substituents tolerated (alkyl, aryl and heteroaryl ketones). a,p-Unsaturated esters, in the case of the intermolecular cyclopropanation, and a,p-unsaturated diimides for the intramolecular reaction, extends the substrate scope of the process (Fig. 2.7). A transition state model for the intramolecular cyclopropanation reaction has been proposed as depicted in Scheme 2.38 for catalyst 65 [106d]. In this model the ammonium salt adopts a conformation that gives the Z-enolate of the nucleophile on deprotonation with the base. The intramolecular conjugate addition of the enolate then takes place through a boat-type transition state. 

Nonconjugated olefins, acetylenes, styrenes, a,P-unsaturated aldehydes, a,P-unsaturated ketones, a,P-unsaturated acids and quinones are all arylated under Meerwein conditions. Conjugated dienes and ene-ynes can be also used as substrates. 

Molecules that have a C=C unit and a C=0 unit in a molecule but are not conjugated are common, but they are not the focus of this chapter. The C=C and C=0 units are connected directly in conjugated carbonyl compounds. Such carbonyl compounds are often known as a,P-unsaturated carbonyl compounds (a,P-unsaturated ketones, a,P-unsaturated aldehydes, a,P-unsaturated esters, etc.). Typical examples include 3-buten-2-one (the common name is methyl vinyl ketone, 10) and 2-propenal (the common name is acrolein, 11). In these molecules, the presence of the carbonyl will influence reactions at the C=C... 

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