Maleic anhydride, cydoaddition with

An interesting approach involving the use of a fluorous dienophile as a diene scavenger under microwave conditions has been investigated by Werner and Curran [101]. The classical Diels-Alder-type cydoaddition of diphenylbutadiene with maleic anhydride as dienophile was accelerated under microwave heating, such that it... 

Cycloaddition reactions proceed generally via the triplet state. However, the charge transfer interaction may be important for the initial photoexdtation. An example is the 1,2-cydoaddition of maleic anhydride with benzene. The benzene-maleic anhydride complex is the photoabsorbing species (76). 

Recently, Ghosez and Beaudegnies [319] recommended chiral azadienes 9.102 derived from a,P-unsaturated aldehydes and Enders s hydrazines 1.76. To observe a high face selectivity in the cydoadditions with maleimides or maleic anhydride conducted at room temperature, the side chain of the hydrazines must be bulky (R = Me) (Figure 9.50). The cleavage of the auxiliary is accomplished with Zn-AcOH, but this also saturates the double bond, and diastereoisomers are formed. Unfortunately, this cydoaddition does not work with acrylates or fu-marates. 

Diels-Alder cydoaddition involving 1,3-dienylboronates was first reported in 1987 [65]. These dienes react with activated dienophiles such as maleic anhydride and maleimides at relatively high temperature (toluene, 80 °C) to give exdusivdy the en-do cydoadducts (Scheme 9.29). A mixture of diastereoisomers was obtained regiose-lectively with methyl acrylate or acrylonitrile. The endo selectivity was sigitificantly increased when the reaction was performed without solvent (66). 

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