Study on Intramolecular Cyclization of Organic Hetero-Containing Enynes Induced by Ruthenium Metal Complexes

• Main Authors: Ji-Xian Lo, 羅濟賢
• Other Authors: Ying-Chih Lin
• Format: Others
• Language: en_US
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/31324575424543749041

碩士 === 國立臺灣大學 === 化學研究所 === 101 === The intramolecular cyclization of 1,8-enyne containing hetero-atom mediated by ruthenium complex, leading to the formation of the oxygen heterocycle is described. In the [Ru]Cl-induced ([Ru] = Cp(PPh3)2Ru) reactions of enyne 1, with an internal methyl group on the olefinic group, the vinylidene complex 3 containing an oxepane moiety, bonded at Cβ is isolated. The reaction proceeds via the formation of an allenylidene intermediate followed by a cyclization at Cγ under mild condition. Stabilization of the cationic charge by the presence of methyl substituents clearly controls the reaction pathway. The reaction of 3 with NaOMe produces the acetylide complex 4. The alkylation of 4 by allyl bromide and methyl iodide as alkylation reagents induced the formation of 5a and 5b, respectively. Heating complex 3 in CH3CN or treatment of 1 with [Ru]NCCH3+ in CHCl3 at 50 °C gave the organic enyne 6 as the cyclized product. Furthermore, the same reaction in CHCl3/MeOH leads to the organic product 7a by tandem cyclization, formed possibly via sequential allenylidene/vinylidene cyclization followed by a nucleophilic addition of a methoxide. In the reaction of [Ru]Cl with enyne 2a, containing two terminal methyl groups on the olefinic parts, the vinylidene complex 8 with a new oxane ring is obtained as a mixture of two diastereoisomers and the anti-isomer is the major product. Mild thermolysis of 2a in CHCl3 at 50 °C in the presence of [Ru]NCCH3+ gave 11a (anti-11a/syn-11a = 2/1). The proposed mechanism is via the formation of a six-membered ring chair-like transition state with the most bulkiest group in the pseudoequatorial position to reduce the 1,3 diaxial interactions. Hence, in the reaction of propargylic alcohol 2b, the isomer ratio was greatly improved to 10:1.8 due to the steric effect of the bulkier cyclopentyl tether. Treatment of 2a with [Ru]NCCH3+ in MeOH afforded two products, the hexahydro isochromene compound 12 with a methoxide group and the carbene complex 13, both containing a newly formed bicyclic ring. The same reaction of 2b in MeOH afforded no corresponding bicyclic ring products, but 11b was obtained. Similarly, the reaction of 8 with NaOMe produces the acetylide complex 9 and alkylation of 9 by allyl bromide as alkylation reagent gives 10.