Ketenes reaction with carbonyl compounds

Lithiation of compound (570) (LAD) followed by reaction with carbonyl compounds yields the derivatives (571) (Equation (93)) <89AP(322)29l>. Diels-Alder reaction of compound (572) with ketene diethylacetal gave compound (573) (Equation (94)) <92CL485>. 

Al ion-exchanged montmorillonite efficiently catalyzes the aldol reactions of silyl ketene acetals with carbonyl compounds and acetals. ... 

Acid type catalysts catalyze cross aldol reaction of silyl ketene acetals with carbonyl compounds and acetals. Aluminum cation and proton exchange montmorillonites are effective catalysts. Although the detailed reaction mechanism is not clear, Bronsted acid sites are considered to be the catalytic sites. 

Thermal [2h-2] cycloaddition reactions of carbonyl compounds were catalyzed by a Lewis acid. The catalyst forms complexes with the carbonyl compounds and enhances the electron-accepting power. The reaction shifts from the delocalization band to the pseudoexcitation band. Catalyzed [2h-2] cycloaddition reactions were observed with acetylenic compounds [28] and ketenes [29-31]. 

Silyloxy esters.l Silyl ketene acetals are known to undergo aldol condensation with carbonyl compounds in the presence of TiCl4 (12,268) to afford (3-silyloxy esters. The same products can be obtained in a one-step reaction of an a,p-unsaturated ester with trimethylsilane and a carbonyl compound in the presence of RhCl3H20. 

Ester homologation. The anion of 1 reacts with carbonyl compounds to form ketene-0,S-acetals (2), which are converted into homologated methyl esters (3) by reaction with methanol in the presence of HgCl2. 

AMol-type reactions. The reaction of ketene silyl ethers with carbonyl compounds... 

Ketene acetals, e.g., 1,1-dimethoxypropene and tetramethoxythylene, generally afford [2 + 2] oxetane cycloadducts with carbonyl compounds including a-diketones. However, the dihydrodioxin [4 + 2] cycloadducts of a-diketones with 1,1-dimethoxypropene and tetramethoxyethylene have been observed in thermal and l wis acid-catalyzed reactions when the [4 + 2] cycloaddition is accompanied by an increase in the stabilization energy of the diketone moiety, e.g., phenanthrene generation [Eq. (53)].220... 

Another method for the preparation of 2-alkylidene-1,3-dithiepanes is the reaction of 2-trimethyl-silyl-l,3-dithiepane with carbonyl compounds, for example the synthesis of (190) (Equation (33)) <83EUP810266>, and ketene thials (192) can also be obtained in the usual manner by dehydro-halogenation of 2-haloalkyl-substituted 1,3-dithiepanes (191) (Equation (34)) <75RTC83>. 

Propiolactones can be synthesized following two routes they can be prepared by the ring closure of 3-substituted acids or by the reaction of ketenes with carbonyl compounds. 

Racemic and optically active a- and 3-substituted poly(3-propiolactones) can be synthesized by the current methods of pol5rmerization. However, the synthesis of a-substituted 3-propiolactones usually involves the ring closure of 3-substituted acids and they are often polymerized with anionic initiators. In contrast, the synthesis of 3-substituted 3-propiolactones is often made by the reaction of ketenes with carbonyl compounds (in the presence of a chiral base to obtain optical purity) and their polymerization proceeds with a cationic or coordinated initiator. 

Lithium acetate (LiOAc)-catalyzed aldol reactions between trimethylsilyl enolates and aldehydes proceed smoothly in anhydrous DMF or pyridine to afford corresponding aldols in good to excellent yields under weakly basic conditions (Scheme 20) (120,121). Obviously, it was further evidence that water could accelerate the aldol reaction of ketene silyl acetals with carbonyl compounds (120). Other lithium salts, for example, lithium pyrrolidone, was also an effective catalyst in the aldol reaction between trimethylsilyl enolates and aldehydes (123). 

Related Systems. The carbanions of related 5,5-thioacetals of formylphosphonates also react with aldehydes and ketones, including Q ,/3-unsaturated aldehydes and ketones, to give the corresponding ketene 5,S-thioacetals (e.g. eq 5 ). Horner-Wadsworth-Emmons reactions of carbonyl compounds with 0,S-thioacetals of formylphosphonates [e.g. (Me0)2P(0)CH-(SMe)0Me] and mono(thio)phosphonates [e.g. (Me0)2P(0)-CH2SMe] are also known. 

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