Iron(III)-catalyzed cyclization of alkynyl aldehyde acetals: experimental and computational studies.
FeCl(3)6 H(2)O- and FeBr(3)-catalyzed Prins cyclization/halogenation of alkynyl aldehyde acetals has been realized with acetyl chloride or bromide as halogen source in dichloromethane to afford 2-(1-halobenzylidene or alkylidene)-substituted five-membered carbo- and heterocycles, and thus provides an alternative route for vinylic C-Cl and C-Br bond formation. Five- to eight-membered cyclic enones were efficiently synthesized by FeCl(3)6.H(2)O-catalyzed intramolecular cyclization of alkynyl aldehyde acetals in acetone under mild conditions. An oxocarbonium species generated in situ is proposed to initiate the reaction, and the target products are formed via vinylogous carbenium cation and oxete intermediates according to DFT calculations. Intermolecular reactions of alkynes and aldehyde acetals were also investigated with 20-40 mol% FeCl(3)6.H(2)O catalyst, and produced alpha,beta-unsaturated enones and chlorinated indene derivatives. The present protocol has applications in the synthesis of carbo-, oxa- and azacycles.
Xu
Tongyu
T
Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, P. R. China.
Yang
Qin
Q
Li
Dongpo
D
Dong
Jinhua
J
Yu
Zhengkun
Z
Li
Yuxue
Y
D000080:Acetals / Q000737:chemistry*; D000447:Aldehydes / Q000737:chemistry; D000480:Alkynes / Q000737:chemistry*; D002384:Catalysis; D020650:Combinatorial Chemistry Techniques; D003500:Cyclization; D005290:Ferric Compounds / Q000737:chemistry*; D054879:Halogenation; D007659:Ketones / Q000138:chemical synthesis* / Q000737:chemistry; D015394:Molecular Structure; D012984:Software
D000080:Acetals; D000447:Aldehydes; D000480:Alkynes; D005290:Ferric Compounds; D007659:Ketones