Intramolecular Ene Reactions. Stereo- and Enantioselective Synthesis of Spirolactams through Thermolysis of Enamino Carboxamides

Stereospecific cyclization reaction of alkenyl esters and amides of ethenetricarboxylate

The stereospecificity of the cyclization reaction of (E)- and (Z)-2-alkenyl esters and amides of ethenetricarboxylate has been examined. The reaction of (E)/(Z)-2-butenyl esters with AlCl3 or FeCl3 gave trans-substituted chlorinated γ-lactone diastereomers stereospecifically. (E)/(Z)-2-butenyl and pentenyl amides undergo an intramolecular ene reaction at room temperature gradually. At 80 °C, the (Z)-alkenyl amides were transformed to cis-substituted ene adducts and the (E)-amides were transformed to cis- and trans-substituted ene adduct mixtures. The reaction of (E)/(Z)-2-alkenyl amides with ZnI2 gave trans-substituted γ-lactam diastereomers stereospecifically along with the ene adducts.

One-pot tandem double-aldol reaction/aza-addition of acetylacetamides and o-phthalaldehyde leading to spiroindan-2,2'-pyrrolidines

A novel domino reaction based on o-phthalaldehyde and 3-oxo-N-arylbutanamide 1 has been developed which allows one-pot and efficient synthesis of structurally complex spiroindan-2,2'-pyrrolidines 2 and 3 with complete regioselectivity and high stereoselectivity from acyclic precursors.

Diastereoselective Intramolecular Alder−Ene Reaction on Chiral Perhydro-1,3-benzoxazines. A Rapid Entry to Enantiopure cis-3,4-Disubstituted Pyrrolidines

Chiral 3-acryloyl-2-vinyl-substituted 1,3-perhydrobenzoxazines derived from (-)-8-aminomenthol participate in an ene reaction leading to 3,4-disubstituted pyrrolidinone derivates with excellent diastereoselectivity. The cycloadducts were transformed into enantiopure 3,4-disubstituted pyrrolidines after elimination of the chiral adjuvant.

Metallic salt promoted radical cyclization of beta-keto carboxamides and their corresponding beta-enamino carboxamides

Substituted lactams and spirolactams were obtained by Mn(III)-induced radical cyclization of unsaturated beta-keto carboxamides. Treatment of the corresponding tertiary enamines under similar reaction conditions and in the presence of K(2)CO(3) afforded the same cyclized products but with inversion of diastereoselectivity. The oxidation of optically pure secondary enamines leads to diastereomeric spirolactams in an approximately 3:1 ratio.