62623-73-8Relevant academic research and scientific papers
Syn-anti isomerization of aldols by enolization
Ward, Dale E.,Sales, Marcelo,Sasmal, Pradip K.
, p. 4808 - 4815 (2007/10/03)
A variety of aldol adducts are shown to undergo efficient syn-anti isomerization in the presence of imidazole by an enolization mechanism. Isomerizations are high yielding and occur with little or none of the usual byproducts arising from competing elimination or retroaldol reactions. Most substrates reach equilibrium within 0.3-3 days at ambient temperature in chloroform, benzene, or dichloromethane containing 0.3-1 M imidazole. The process is particularly facile for aldols derived from tetrahydro-4H-thiopyran- 4-one with rate constants for equilibration varying over ca. 1 order of magnitude for the adducts studied; structurally related aldols derived from cyclohexanone isomerized ca. 3-4 times slower. Isomerization of the acyclic aldol 5-hydroxy-4-methyl-5-phenyl-3-pentanone required heating to 60 °C but was achieved with minimal (A methoxymethyl ether derivative isomerized 30-40 times slower than the parent aldol. Isomerization of α,α′-disubstituted aldols and α,α′-bisaldols indicated low regioselectivity in the enolization. The synthetic utility of the process was demonstrated with the effective preparation of aldol stereoisomers unobtainable by direct methods.
1,2-Addition of dimethyl(phenyl)silyllithium to cyclic α,β-unsaturated ketones and regiospecific generation of cyclic silyl enol ethers through Brook rearrangement of the 1,2-addition products
Koreeda,Koo
, p. 831 - 834 (2007/10/02)
A highly convenient two-step sequence for the regiospecific synthesis of cyclic silyl enol ethers has been developed involving the 1,2-addition of dimethyl(phenyl)silyllithium to cyclic α,β-unsaturated ketones followed by the treatment of the resulting silyl carbinols with a catalytic amount of NaH in THF at 25°C.
Reaction of α-Halogeno Ketones with Carbonyl Compounds Promoted by CeI3, CeCl3-NaI,or CeCl3-SnCl2
Fukuzawa, Shin-ichi,Tsuruta, Takuya,Fujinami, Tatsuo,Sakai, Shizuyoshi
, p. 1473 - 1478 (2007/10/02)
Reaction of α-halogeno ketones with aldehydes in the presence of CeI3 in tetrahydrofuran is found to give α,β-unsaturated ketones in excellent yields under mild conditions.In contrast, treatment of α-halogeno ketones and carbonyl compounds with CeCl3-NaI or CeCl3-SnCl2 affords β-hydroxy ketones in good yields.It is assumed that these reactions proceed via cerium enolates.The combined reagents, however, cannot be applied to a Reformatsky-type reaction.Regiospecific and aldehyde chemoselective aldol synthesis are also described.
Fluoride Ion Catalyzed Aldol Reaction between Enol Silyl Ethers and Carbonyl Compounds
Nakamura, Eiichi,Shimizu, Makoto,Kuwajima, Isao,Sakata, J.,Yokoyama, K.,Noyori, R.
, p. 932 - 945 (2007/10/02)
A new aldol reaction effected by the reaction of enol trimethylsilyl ethers and a quarternary ammonium fluoride is reported.Under the influence of a catalytic amount of tetrabutylammonium fluoride at low temperatures, enol silyl ethers react with various aldehydes to give the corresponding aldol trimethylsilyl ethers in fair to good yields.The silyl group of these products can be smoothly removed under mild conditions.Ketones, epoxides, and esters do not serve as electrophiles in this reaction.The reaction proceeds in a regiospecific manner with respect to the enol silyl ethers; the reactions of two regioisomers of 2-methylcyclohexanone with benzaldehyde cleanly give the respective regioisomeric aldol products.The reaction of 4-tert-butyl-1-methyl-2-(trimethylsiloxy)cyclohexene proceeds exclusively by the axial attack of the electrophile, making a strong contrast with the related cases reported on this cyclohexanone system.The aldol addition of a ketone and an aldehyde can be performed without the isolation of the enol silyl ether of the ketone by effecting both the silylation of the ketone and the aldol reaction with the aid of a fluoride anion.The characteristic behavior of the enolate species in this reaction can be rationalized by considering a mobile equilibrium in which the combination of fluorotrimethylsilane and a quarternary ammonium enolate functions as key controlling factor.
