Mechanisms of cascade reactions in the syntheses of camptothecin-family alkaloids: intramolecular [4(+) + 2] reactions of N-arylimidates and alkynes.
The key steps of cascade reactions employed in the syntheses of camptothecin-family alkaloids by Fortunak and Yao are intramolecular aza-Diels-Alder (IADA) reactions between in situ generated N-arylimidates and alkynes. The efficiencies of the IADA reactions are different but not well-understood. DFT calculations shown here provide insights into these two IADA reactions and well-rationalize why hexaphenyloxodiphosphonium triflate (Hendrickson reagent) as an amide-activating reagent is superior to trimethyloxonium fluoroborate.
Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Bioorganic Chemistry and Molecular Engineering of Ministry of Education, College of Chemistry, Peking University, Beijing 100871, China.
Yong
Y
Liang
Xing
X
Jiang
Zhi-Xiang
ZX
Yu
D000480:Alkynes / Q000737:chemistry*; D002166:Camptothecin / Q000138:chemical synthesis* / Q000737:chemistry; D003198:Computer Simulation; D018360:Crystallography, X-Ray; D003500:Cyclization; D007096:Imidoesters / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D015394:Molecular Structure; D013237:Stereoisomerism
D000480:Alkynes; D007096:Imidoesters; D002166:Camptothecin