Cyclization and Cycloisomerization Reactions of O-Containing Aromatic Enynes Consisting of Propargyl Alcohol or Simple Terminal Alkyne Catalyzed by Ruthenium Complexes
Date Issued
2014
Date
2014
Author(s)
Lai, Ying-Hsuan
Abstract
The intramolecular cyclization of aromatic enyne containing oxygen-atom mediated by ruthenium complex, leading to the formation of the oxygen heterocycle is described. Ruthenium complex [Cp(PPh3)2Ru]Cl assisted cyclization of two propargylic alcohols 1 and 7a each containing two terminal methyl groups on the olefinic parts yielded the vinylidene complexes 2 and 8 with a new six-membered and five-membered ring, respectively, in CH2Cl2 among other products. In MeOH, tandem cyclization of 1 yielded the organic compound 5a and the carbene complex 4 with a 6H-benzo[c]chromene moiety. Similarly, 12a with a tetrahydrodibenzo[b,d]furan moiety was obtained from 7a; however, with no comparable carbene complex. The unit reactions yielding these 6H-benzo[c]chromene and tetrahydrodibenzo[b,d]furan species may proceed via a first cyclization reaction between propargylic alcohol and alkenes through the allenylidene intermediate giving vinylidene species followed by second cyclization between Cα and the terminal carbon of the vinyl group.
Unlike the reactions of 1 and 7a, the 1,7-enyne 7b containing no methyl group on the olefinic part underwent enyne cycloisomerization involving skeletal rearrangement when catalyzed by [Ru]NCCH3+ in a co-solvent of CHCl3 and MeOH to yield the product 15a with an addition of methoxy group. The cycloisomerization reaction proceeds via a bidentate coordination of enyne to ruthenium metal and then the reaction is followed by an oxidative cyclometalation to give metallacyclopentene involving a β-oxygen elimination via disruption of both C-O bond and Ru-Cα bond to form a double bond between Cα and Cβ to generate the zwitterionic intermediate. And then, the reaction proceeded to undergo rearrangement and addition of methoxy group to produce 24.
Treatment of ethynylbenzene 22a containing a vinyloxy group at the ortho position of the aryl ring with a catalytic amount of [Ru]Cl in the presence of KPF6 in a co-solvent of CH2Cl2/ROH (R = Me, Et, i-Pr) for 16 h afforded yellow oil 23a-c containing benzoxepine with addition of an alkoxy group. The formation of 23a is via generation of vinylidene complex and subsequent [2+2] cycloaddition of vinylidene Cα=Cβ bond with the olefin on vinyloxy group to give bicyclic carbene complex followed by addition of an alkoxy group to disrupt the C-C bond. In addition, changing the substituent on the vinyl group, such as that in 22b, also produced the corresponding benzoxepine derivatives. In CH2Cl2, cycloisomerization of 22a gave the carbene complex 24. The reaction involved generation of a vinylidene complex followed by a subsequent [2+2] cycloaddition of vinylidene Ru= Cα bond with an olefin on vinyloxy group. And then, the reaction proceeded to undergo skeletal rearrangement to produce 24.
Subjects
釕金屬
丙炔醇
烯炔
催化
苯並吡喃
苯並呋喃
苯並噁庚因
環化反應
環異構化反應
Type
thesis
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