Reaction of pyrazole with phenethyl bromide

A very important microwave-specific effect was evidenced in the absence of a base for the reaction of pyrazole with phenethyl bromide (reaction times MW = 8 min, A = 48 h, Eq. 41). When the same reaction was performed in the presence of KOH, the microwave effect disappeared (vide supra, Eq. 26). 

Reaction of pyrazole with phenethyl bromide 84 Ring opening of an epoxide by amines 85... 

Reaction of pyrazole with phenethyl bromide In the absence of base, the phenethy-lation of pyrazole under solvent-free conditions is more rapid by far under the action of microwaves (8 min at 145 °C) compared with A, which requires 48 h... 

The reaction of pyrazole with phenethyl bromide [72] (Scheme 11.19) gave the product in the absence of base, and the time consumed in microwave irradiation was 8 min as compared to conventional heating that took 48 h, but for the same reaction the presence of base KOH overruled the microwave effect. The yield with KOH was 64% in microwave irradiation and 61% with conventional heating at 145 °C for 8 min. This was because of the availability of a loose ion pair at the reactive species and weak evolution of polarity between transition state and reactant molecules. 

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