Intramolecular ene reactions. 7. Asymmetric induction in intramolecular ene reactions of chiral 1,7-dienes: a diastereo- and enantioselective synthesis of substituted cyclohexanes
Asymmetric induction in intramolecular ene reactions of 1,7-dienes
作者:Lutz F Tietze、Uwe Beifuss
DOI:10.1016/s0040-4039(00)84369-5
日期:1986.1
Lewis-acid catalyzed intramolecularenereactions yielding trans-cyclohexanes 7a-d and 8a-d. The extent of diastereoselectivity depends on the reaction temperature. The 1,7-dienes 6 are obtained via Knoevenagel condensation of citronellal 5 with acyclic 1,3-dicarbonyls and analogous compounds 4. Starting with the diene 6e, however, an intramolecular hetero-Diels-Alder reaction takes place.
New and Efficient Lewis Acid Catalysts in Intramolecular Ene Reactions
作者:Lutz F. Tietze、Uwe Beifuß
DOI:10.1055/s-1988-27573
日期:——
The thermal or Lewis acid catalyzed intramolecular ene reaction of the Knoevenagel adduct 3 from citronellal and dimethyl malonate affords the two diastereoisomeric dimethyl (5-methyl-2-trans-isopropenylcyclohexyl)malonates 4a and 4b. Anhydrous iron(III) chloride on basic alumina proved to be the best catalyst giving, at - 78°C, the two diastereoisomers 4a and 4b in a ratio of 98.8:1.2 in 92% yield.
Surface-Mediated Reactions. 6. Effects of Silica Gel and Alumina on Acid-Catalyzed Reactions
作者:Paul J. Kropp、Gary W. Breton、Stephen L. Craig、Scott D. Crawford、William F. Durland、John E. Jones、J. Scott Raleigh
DOI:10.1021/jo00118a035
日期:1995.6
Adsorption of a variety of acids to chromatographic silica gel results in substantial enhancement of their catalytic activity-affording easily prepared, environmentally benign heterogeneous acids that are highly effective in mediating a number of processes. This was shown for the isomerization of allene 1 and dimerization of the corresponding 1,3-diene 2; cyclization of (R)-citronellal (5), the related diester 10, and 1,5-cyclooctadiene (15); Rupe rearrangement of alkynol 18; and Friedel-Crafts cyclodehydration of alcohols 21. By contrast, commercially available Nafion-H was significantly less effective as a heterogeneous acid catalyst. Chromatographic alumina displayed enigmatic behavior, showing enhanced acidity on the adsorption of HCl but little or no acidity on the adsorption of a variety of other types of acid. The results are discussed in terms of the surface structures of silica gel and alumina.