A theoretical study on the trans-addition intramolecular hydroacylation of 4-alkynals catalyzed by cationic rhodium complexes.
The mechanism of the intramolecular hydroacylation reaction of 4-alkynals is studied for a 4-pentynal-[Rh(PH2CH2CH2PH2)]+ model system using MP2 calculations. The endo-cyclization to form a rhodacyclohexenone intermediate is kinetically less favorable than the exo-cyclization to form a rhodacyclopentanone intermediate. The kinetic preference toward the endo-cyclization is found to be enhanced by complexation of donor ligands (H2CO, NCH, and HCCH). The formation of cyclopentenone product proceeds via reductive elimination from one of the two rhodacyclohexenone intermediates, whereas the formation of cyclobutanone product from the two rhodacyclopentanone intermediates requires high activation energy. Addition of an acetylene stabilizes the highly electron-poor rhodacyclopentanone intermediate generated from exo-cyclization and leads to an insertion to give [4 + 2] annulation product, cyclohexenone. The role of a coordinating acetone solvent in the formation of cyclopentenone product is also discussed.
Chung
Lung Wa
LW
Department of Chemistry and Open Laboratory of Chirotechnology of the Institute of Molecular Technology for Drug Discovery and Synthesis, The Hong Kong University of Science & Technology, Clear Water Bay, Kowloon, Hong Kong, China.
Wiest
Olaf
O
Wu
Yun-Dong
YD
D000215:Acylation; D000447:Aldehydes / Q000138:chemical synthesis* / Q000737:chemistry; D000480:Alkynes / Q000737:chemistry*; D002384:Catalysis; D002412:Cations / Q000737:chemistry; D003198:Computer Simulation; D003500:Cyclization; D007659:Ketones / Q000138:chemical synthesis* / Q000737:chemistry; D007700:Kinetics; D008956:Models, Chemical; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D012238:Rhodium / Q000737:chemistry; D013237:Stereoisomerism
D000447:Aldehydes; D000480:Alkynes; D002412:Cations; D007659:Ketones; D009942:Organometallic Compounds; D012238:Rhodium