Intramolecular Heck Reaction on the Synthetic Route to Baccatin III

1 Intramolecular Heck Reaction on the Synthetic Route to Baccatin III 

Insertion of Pd(0) into the allyUc C=C-OTf bond was followed by the formation of the Jt-complex with the second C=C bond, transient formation of a Pd-C bond and final hydride elimination to close the catalytic cycle. 

Generally, the Heck reaction requires elevated temperatures. With the specific, highly functionalized substrate 13, the reaction was successfully achieved at 90°C in MeCN. To the author s great satisfaction, it proceeded with an acceptable yield, forming exclusively the 8-membered ring in 14. The subsequent final steps in the synthesis of baccatin III (15) have been reported repeatedly [17,18]. 

2 Trifunctional Catalyst for Biomimetic Synthesis of Chiral Dials Synthesis of the Paclitaxel Side-Chain 

This catalytic system allows three independent transformations to occur in sequence the Heck reaction, N-oxidation and asymmetric dihydroxylation (AD). The mechanism of the Heck reaction is discussed in the previous section. Here we take a closer look at the last two steps. They are coupled processes, based on the Sharpless asymmetric dihydroxylation reaction [22, 23]. Several recent reviews on Sharpless asymmetric dihydroxylation cover the general synthetic aspects [24-27], together with methods for immobilization of the osmium catalysts [28]. 

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