No abstract

Two electron-deficient dienes were reacted with a series of twelve electron-poor and electron-rich dienophiles to give, in some cases, the corresponding Diels-Alder adducts. Clear differences in the roles played by the two frontier orbital interactions emerged. It was demonstrated that in the case of normal Diels-Alder cycloadditions, the FMO theory could predict the relative reactivities between dienophiles, while in the case of inverse-electron demand Diels-Alder reactions, it could not. It was shown that the dissymmetry in electron-rich dienophiles increases their reactivities.

[reaction: see text] Homochiral alpha-amino acids, heterocycles, and carbocycles are efficiently constructed via a short sequence of reactions starting from the chiral auxiliary p-menthane-3-carboxaldehyde. The key feature of the sequence is a highly selective tandem Mitsunobu/3,3-sigmatropic rearrangement of hydrazoic acid that procures enantiomerically enriched allylic azides. The sequence is either terminated by oxidative cleavage to provide amino acids or by ring-closing metathesis to provide heterocycles or carbocycles bearing nitrogen.

Highly hindered and sensitive isocyanates react with alcohols under mild catalysis by titanium tetra-t-butoxide to give high yields of the corresponding carbamates.

The base-catalyzed cycloaddition and double Michael cyclization of substituted Nazarov reagents and of l-phenylsulfinyl analogs, with 2-carbomethoxy-2-cyclohexen-I-one 1 yielding cis-decalins is reported. The reaction is highly stereoselective affording cis,cis-or cis,trarls-decalins. Mechanistic aspects are briefly discussed. On dCcrit la cycloaddition catalysCe par des bases des rCactifs de Nazarov substituks, ainsi que d'un analogue 1-phCnylsulfinylC, avec la 2-carbomCthoxy-2-cyclohexenone 1 produisant des cis-dCcalines. La rkaction est hautement stCrCosClective generant des cis,cis-ou cis,trarzs-dCcalines. Les mkcanisrnes de ces reactions sont brikvement discutes. JEAN-FRANCOIS L