Fluorous dienophile

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... 

Scheme 7.88 Diene scavenging utilizing a fluorous dienophile.

Another interesting development is the use of fluorous-based scavengers in conjunction with microwave synthesis and fluorous solid-phase extraction (F-SPE) for purification. This was recently illustrated by Werner and Curran [74] in their investigation of the Diels-Alder cycloaddition of maleic anhydride to diphenylbutadiene (Scheme 11.23). After performing microwave-assisted cycloaddition (160 °C, 10 min) with a 50% excess of the diene, the excess diene reagent was scavenged by a structurally related maleimide fluorous dienophile under the same reaction conditions. Elution of the product mixture from an F-SPE column with Me0H-H20 provided the desired cycloadduct 89 in 79% yield and 90% purity. Subsequent elution with diethyl ether furnished the fluorous Diels-Alder cycloadduct. 

Proline analogs, biaryl-substituted, fluorous synthesis 112 PS-anthracene, dienophiles 151 PS-carbodiimide 136 Pimine C-2, nucleophilic displacement 119... 

Scheme 8.54 Application of a fluorous-supported dienophile as a scavenger for dienes.

The effect of the composition of the fluorous solvent (from pure perfluoro-benzene to pure perfluorohexane) was investigated observing higher yields in the cycloaddition products with higher fluorous content of the solvent, with a plateau region at approximately 50 50 perfluorobenzene perfluorohexane this is because of increased association constant of the capsule. The study was further extended to other combinations of dienes and dienophiles, showing in all cases increases from 2.3- to 21-fold in the experiments carried out in the presence of... 

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