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.
Liang
Yong
Y
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.
Jiang
Xing
X
Yu
Zhi-Xiang
ZX
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