Polymer-supported phosphazene base PS-BEMP

Fig. 7.8 Polystyrene-bound dehydrating agent (left) and polymer-supported phosphazene base PS-BEMP (right) utilized for oxadiazole synthesis.

In the same publication, it was reported that this cyclo-dehydration could also be affected by using tosyl chloride and the polymer-supported phosphazene base PS-BEMP, and again, microwave heating was found to be advantageous (Scheme 6.25). In utilising this protocol, no scavenger purification strategy was deemed necessary and the authors note that this is the most efficient 1,3,4-oxadiazole synthesis of the three polymer-supported methods described. 

Scheme 18.4). For preparation of the C/D spiroketal fragment (9), we needed to transform the chloroepoxide (5) to a second homologated epoxide (8) via an intermediate chlorohydrin (6) (Scheme 18.4). Solution-phase bases were used initially but led to alternative aUyUc alcohol products however, the polymer-supported phosphazene base (7 PS-BEMP) was more successful and allowed the epoxide (8) to be isolated following filtration in 87% yield. 

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