Theoretical Study on Pd-Catalyzed Acylation of Allylic Esters with Acylsilanes and Acylstannanes

Acylation of allylic esters with acylsilanes and acylstannanes in the presence of a palladium complex was investigated theoretically using the DFT (B3PW91) method. We examined along the reaction that was reported by Tsuji’s. In this mechanism for generating active species, a Pd dinuclear complex 5 (the reaction of Pd and 2) was produced. Then, 5 is decomposed to two mononuclear complex 6. The reaction of 6 and 1 forms an intermediate 7, which is active species. In catalytic cycle from 7, the O (1) atom of 7 attacks the Si or Sn atom in TS7-8 to produce 8. Then, the C(1)-C(2) reductive elimination from 8 occurs through the TS8-9 to yield 9. Therefore, 9 decomposed to Pd(0), 3 and 4. However, reaction mechanism from 9 to 6 should be considered because Pd(0) + 3 + 4 are less stable than 9 by 29.2 kcal/mol, 9 does not decompose. We proposed the reaction mechanism from 9, as shown below: 1) 2 attacks 9 to form 10. 2) 10 released 4 to produce a five coordinated intermediate 11. 3) 11 changes its structure to another π-allyl complex 12. 4) The product 3 was released from 12 and 6 formed again for a next catalytic cycle. The rate-determining step of these reaction is nucleophilic attack of carbonyl oxygen to RA (7 → 8), and the △G≠ for I, II and III was calculated to be 27.1, 39.1, and 30.9 kcal/mol, respectively. As a result, we elucudated the reaction mechanism of acylation of allylic esters with acylsilanes and acylstannanes in the presence of a palladium complex.