54323-00-1Relevant articles and documents
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.
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.
