New and effective synthesis of 7-triethylsilylbaccatin III from 7 beta,13 alpha-bistriethylsiloxy-1 beta,2 alpha,10 beta-trihydroxy-9-oxo-4(20),11-taxadiene

7 beta,13 alpha-Bistriethylsiloxy-1 beta,2 alpha,10 beta-trihydroxy-9-oxo-4(20), 11-taxadiene (2), derived from 10-deacetylbaccatin III via degradation of oxetane ring, was conveniently converted into 7-triethylsilylbaccatin III (1) by way of a new and effective method for constructing oxetane ring. Thus, the synthesis of a precursor of taxol from novel taxoid 2 was accomplished.