Exploration of high-pressure cycloadducts of furans and citraconic anhydride as precursors for CD-ring fragments of paclitaxel and its analogues
Beusker PH, Aben RWM, Seerden JPG, Smits JMM, Scheeren HW
EUROPEAN JOURNAL OF ORGANIC CHEMISTRY (11): 2483-2492 NOV 1998

Abstract:
The high-pressure promoted Diels-Alder reactions between several furans and citraconic anhydride have been studied and the cycloadducts obtained have been explored in new straightforward routes to the CD-ring fragment of paclitaxel. The reaction between furan and citraconic anhydride afforded the exo cycloadduct diastereoselectively, whereas a variety of 2-substituted furans afforded approximate 1:1 mixtures of exo regioisomers. Separation of both regioisomers was accomplished after either diastereoselective esterification or regioselective reduction of the anhydride function. Ether cleavage of the bicyclic compounds by either high-pressure promoted ether cleavage or Boord elimination afforded several potential CD-ring precursors which can be used in the total synthesis of paclitaxel analogues.