Diethyl fumarate, addition cycloaddition with

The thermal Diels-AIder reactions of perfluorocyclopentadiene with diethyl maleate and diethyl fumarate have been shown to proceed in accordance with the cis principle enunciated by Alder and Stein. Further evidence for the normal behaviour of perfluorocyclopentadiene in such 1,4-additions is provided by the observation that hydrolysis of the amide produced by treatment of the diene with A-allyltrifluoroacetamide at 50 °C yields the azatri-cyclononane (19) (see Scheme 4) obviously, Alder s endo rule applies to this cycloaddition. The same technique has been used to show that the Diels-AIder adduct obtained from perfluorocyclohexa-1,3-diene and A-allyltri-fluoroacetamide at 110°C is predominantly or even exclusively the endo-isomer. ... 

If the diethyl esters, instead of dimethyl fumarate or maleate, are used with 3,3-dimcthoxycy-dopropene, there is no codimerization at temperatures below 60 C. At 90-110°C, the reaction can be forced to proceed but, even in the absence of catalyst, a thermal cycloaddition occurs. The ortho ester 25b is formed as the result of a thermal degradation of the primary adduct. Methanol formed during the degradation process is trapped by unchanged primary product 23b. Additional side products are also formed in the reaction. 

This group " also diverted the usual Diels-Alder cycloaddition pathway of Reissert salts with olefinic esters to a 1,3-dipolar cycloaddition pathway by the addition of triethylamine. Thus treatment of munchnone imine 364 with ethyl acrylate and triethylamine affords the 1,3-dipolar cycloaddition product 366 (30%) as the major product, formed by fragmentation of cycloadduct 365 (Fig. 4.121). The Diels-Alder product (not shown) is formed in 15% yield. Similar products to 366 are formed with dimethyl and diethyl maleate and fumarate. Laude and coworkers " also were able to trap munchnone imine 367 with dipolarophiles to furnish 368 (Fig. 4.122). No Diels-Alder cycloadducts derived from the oxazolium salt were detected. In contrast, fumarate and acrylate esters give only Diels-Alder cycloadducts from the tautomeric oxazolium salt (not shown). However, benzo-quinones and 1,4-naphthoquinone react in a 1,3-dipolar fashion with munchnone imine 372 derived from Reissert compound 369 to give 373 (Scheme 4.11). " Diels-Alder cycloadducts derived from oxazolium salt 371 were not observed. In a... 

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