Alternative esters in the synthesis of ZD0947

Alternatives to the original iso-borneol and allyl esters were investigated in the synthesis of ZD0947 (1). Homologous allylic esters were prepared in higher yields and were more readily purified than for the existing route, but offered no further benefits later in the synthesis. However, the PNB-substituted ester series provided crystalline intermediates, higher yields and simplified isolations through-out, and utilised a heterogeneous hydrogenation, thus reducing the residual catalyst levels.