1.2- Dienes, cycloaddition

As the name implies it is related to the diene cycloaddition reaction, the Diels-Alder reaction. The ene component the olefin with the allylic hydrogen, takes much the same part as the diene in the Diels-Alder reaction. 

The periselectivity of the tropone-diene cycloaddition is dependent on the reaction temperature. The exo [6 + 4] cycloadduct is considered to be the kinetic product, the endo [4 + 2] cycloadduct being the thermodynamic product291. 

Hudlicky et al. (65) reported a formal stereoselective total synthesis of the oxygenated pyrrolizidine alkaloids platynecine (336), dihydroxyheliotridane (337), hastanecine (341), and tumeforcidine (342), involving an intramolecular azide-diene cycloadditions (Scheme 9.65). Intramolecular 1,3-dipolar cycloaddition of... 

The formation of polysubstituted cycloheptadienones depicted in Eq. (5.334) constitutes the first example of an acid-induced ketene-diene cycloaddition.908... 

With cyclic electron-deficient dienes, cycloaddition reactions are generally elTicient, in particular with electron-rich dienophiles. Methyl 2-oxo-6-(trifluoromethyl)-2/f-pyran-4-carboxylate (8) reacts with various alkenes to give cycloadducts. Only one regioisomer is obtained, in agreement with the prediction from orbital coefficients (Table 4). ... 

Clearly, the utilization of the [6 + 4] tropone-diene cycloaddition for synthetic applications has just begun to develop and many new opportunities for exploiting the unique combination of stereocontrol and synthetic convergency afforded by these reactions is certain to be forthcoming in the near future. 

Diene cycloaddition reactions have frequently been used to characterize relatively unstable arene oxide-oxepins. The reactions of 1 with maleic anhydride or dimethyl... 

Danishefsky has used the imine-diene cycloaddition reaction (Scheme 3) (85TL5983). Reaction of Hagemann s ester 18 with dihydro-)3-carboline 14 in chloroform without catalyst afforded 50% of the pentacyclic lactam 19. Reduction of 19 with lithium aluminum hydride followed by acidic hydrolysis gave the known yohimbine derivative 20. 

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