Asymmetric Diels–Alder reaction: comparison of menthoxyaluminium and lanthanide chiral catalysts
作者:Miguel Quimpère、Krzysztof Jankowski
DOI:10.1039/c39870000676
日期:——
Some dihydropyran carboxylates synthesized via the Diels–Alderreaction with chiralcatalysts display an enantiomeric excess of up to 16% for menthoxyaluminium and up to 64% for chirallanthanidecatalysts.
Konowal,A. et al., Roczniki Chemii, 1968, vol. 42, p. 2045 - 2059
作者:Konowal,A. et al.
DOI:——
日期:——
The conformation oft-butyl 2-methoxy-5, 6-dihydro-2H-pyran-6-carboxylates and 6,6′- disubstituted 2-methoxy-5,6-dihydro-2H-pyran derivatives on the basis of1H and13 C NMR spectra
AbstractThe 1H and 13C NMR spectra of trans‐ and cis‐tert‐butyl 2‐methoxy‐5,6‐dihydro‐2H‐pyran‐6‐carboxylates (1 and 2) and 6,6′‐disubstituted 2‐methoxy‐5,6‐dihydro‐2H‐pyrans (3‐7) have been recorded. HH and CH coupling constants are discussed in terms of the 1H6⇄6H1 conformational equilibrium. It has been found that 1 occurs exclusively in the 1H6 conformation, whereas its cis isomer, 2, exists in an equilibrium of both half‐chair forms. 6,6′‐Disubstituted 2‐methoxy‐5,6‐dihydro‐2H‐pyrans 3‐6 display spectral and conformational behaviour similar to that of 1, whereas 7 resembles 2 in this respect.
Efficient Organocatalytic Hetero-Diels-Alder Reactions of Activated Ketones under High Pressure for Direct Access to δ-Lactones¹
A general and efficient protocol for the high-pressure-promoted hetero-Diels-Alder reactions of activated ketones has been developed. The reactions are successfully achieved by thiourea-derived organocatalysts, and the desired adducts, convenient precursors of δ-lactones, are obtained in good to high yields.