The Beckmann rearrangement of cyclohexanone oxime was achieved by the combined use of cobalt salt and Lewis acids co-catalysts (each 10 mol%). Various combinations of cobalt salts and Lewis acids gave lactams in a sat...The Beckmann rearrangement of cyclohexanone oxime was achieved by the combined use of cobalt salt and Lewis acids co-catalysts (each 10 mol%). Various combinations of cobalt salts and Lewis acids gave lactams in a satisfactory yield under mild conditions. This method makes it possible to reduce undesirable byproducts.展开更多
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 T...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.展开更多
Beckmann rearrangements of oximes to lactams often require harsh conditions and/or the use of large amounts of acid catalyst. To reduce the amount of Bronsted acid required, and to avoid the formation of a large amoun...Beckmann rearrangements of oximes to lactams often require harsh conditions and/or the use of large amounts of acid catalyst. To reduce the amount of Bronsted acid required, and to avoid the formation of a large amount of undesirable byproducts under mild reaction conditions, a low environmental load process was developed. Beckmann rearrangements of cyclohexanone oxime and cyclooctanone oxime were achieved using a combination of a Bronsted acid and cobalt tetra-fluoroborate hexahydrate. Various Bronsted acid catalysts (10 - 20 mol%) were used to obtain the corresponding lactams in high yields at 80℃.展开更多
文摘The Beckmann rearrangement of cyclohexanone oxime was achieved by the combined use of cobalt salt and Lewis acids co-catalysts (each 10 mol%). Various combinations of cobalt salts and Lewis acids gave lactams in a satisfactory yield under mild conditions. This method makes it possible to reduce undesirable byproducts.
文摘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.
文摘Beckmann rearrangements of oximes to lactams often require harsh conditions and/or the use of large amounts of acid catalyst. To reduce the amount of Bronsted acid required, and to avoid the formation of a large amount of undesirable byproducts under mild reaction conditions, a low environmental load process was developed. Beckmann rearrangements of cyclohexanone oxime and cyclooctanone oxime were achieved using a combination of a Bronsted acid and cobalt tetra-fluoroborate hexahydrate. Various Bronsted acid catalysts (10 - 20 mol%) were used to obtain the corresponding lactams in high yields at 80℃.
