Dimethylaluminum methide complex Tf2CHAlMe2: an effective catalyst for Diels–Alder reaction of α,β-unsaturated lactone derivatives with cyclopentadiene
作者:Hikaru Yanai、Arata Takahashi、Takeo Taguchi
DOI:10.1016/j.tet.2007.09.061
日期:2007.12
catalyst system for the catalytic DA reaction of less reactive α,β-unsaturated lactone derivative with cyclopentadiene (CP). In this catalyst system, Tf2CHAlMe2 is an active species and an excess amount of Me3Al plays an important role to lower the catalyst loading. Substituent effect of the lactone framework on π-facial selectivity was also examined. In the reactions of both γ-substituted 5-membered lactone
DBU-Catalyzed Deconjugation of 7-Substituted 3,4-Didehydro-2-oxepanones. Deuterium Incorporation, Significance of the Imine Double Bond, and Application to the Synthesis of a Key Pharmacophore
作者:Duraiswamy A. Jeyaraj、Kamal K. Kapoor、Veejendra K. Yadav、Harsh M. Gauniyal、Masood Parvez
DOI:10.1021/jo971417z
日期:1998.1.1
7-Substituted 3,4-Didehydro-2-oxepanones are conveniently deconjugated to the 4,5-didehydro derivatives by DBU. The isomerization of 7-benzyl-substituted 2-oxepanones proceeds to the extent of 90% over the initial 3 h; the concentration falls gradually thereafter to achieve, in 25 h, a 3:2 equilibrium in favor of deconjugation. Such an equilibrium does not exist for the 7-methyl and the 7-(2-phenethyl) derivatives. The significance of the imine double bond in DBU has been explored. The isomerization in CDCl3 causes deuterium incorporation at positions 3 and 5 of the 2-oxepanones examined and at position 6 of DBU. The mechanistic rationales for these deuterium incorporations are advanced. The transformation of 7-benzyl-3,4-didehydro-2-oxepanone into a bicyclo[3.3.0] skeleton that is present in a diverse class of biologically active natural products is described as a possible potential use of the present deconjugation methodology.
Chiral 6,7-dihydrooxepin-2(5H)-ones and the azepinone analogues: Conformation and diastereofacial selectivity in addition to the enones
Diastereofacialselectivity in addition to the enones of 6-and 7-substituted dihydrooxepinones was studied. The addition occurred preferentially from the face anti to the substituent and 7-substituted substrates showed higher diastereofacialselectivity than the 6-substituted substrates. An explanation for the observed diastereofacialselectivity is proposed.