Asymmetric aldol reactions. A new camphor-derived chiral auxiliary giving highly stereoselective aldol reactions of both lithium and titanium(IV) enolates
作者:Mary Pat Bonner、Edward R. Thornton
DOI:10.1021/ja00004a034
日期:1991.2
camphor-derived N-propionyloxazolidinone effects asymmetric stereochemical control in syn-selective aldol condensations of the derived lithium and titanium (IV) enolates with a variety of aldehydes. Simple and diastereofacial selectivities of the reaction are high, and diastereomeric purities of the crude aldol adducts can be improved, usually by a single recrystallization, to levels of 98-99% in most cases
Acyclic stereoselection. Part 42. 1,4- and 1,5-Stereoselection by sequential aldol addition to a .alpha.,.beta.-unsaturated aldehydes followed by Claisen rearrangement. Application to total synthesis of the vitamin E side chain and the archaebacterial C40 diol
作者:Clayton H. Heathcock、Bruce L. Finkelstein、Esa T. Jarvi、Peggy A. Radel、Cheri R. Hadley
DOI:10.1021/jo00244a017
日期:1988.4
Asymmetric aldol reactions: a novel model for switching between chelation- and non-chelation-controlled aldol reactions
作者:Tu Hsin Yan、Chang Wei Tan、Hui Chun Lee、Hua Chi Lo、Tzung Yu Huang
DOI:10.1021/ja00060a010
日期:1993.4
A new camphor-based N-propionyloxazolidinethione provides remarkable levels of asymmetric induction for both chelation-and non-chelation-controlled aldol processes. While the aldol condensation of the derived di-n-butylboryl enolate with various aldehydes affords the 'Evans'' syn aldol with excellent diastereoselectivity, the chlorotitanium enolate gives the ''non-Evans' syn aldol expected from chelation control. Most noteworthy is the observation that the sense of facial selectivity from the chlorotitanium enolate of propionyloxazolidinethione is opposite to that obtained from propionyloxazolidinone. This important finding illustrates the importance of increased chelating potential of the enolate ligand, ring thiocarbonyl, in maximizing the aldol pi-facial discrimination. Final nondestructive chiral auxiliary removal via hydroperoxide-assisted hydrolysis and subsequent esterification provides enantiomerically pure methoxy-carbonyl aldols.
BONNER, MARY PAT;THORNTON, EDWARD R., J. AMER. CHEM. SOC., 113,(1991) N, C. 1299-1308
The decarboxylative E′-dehydration of β,γ-unsaturated δ-hydroxy acids with DMF-dineopentylacetal shows SYN-faciality irrespective of whether the conformation of the hydroxy group relative to the double bond axis is anticlinal or synclinal.