Tandem cyclization of enynes containing a thioether or ether linkage via ruthenium allenylidene and vinylidene complexes
Journal
Organometallics
Journal Volume
32
Journal Issue
21
Pages
6379-6387
Date Issued
2013
Author(s)
Abstract
The two aromatic S-enynes HCî - CCH(OH)(C6H 4)SCH2C(R)=CH2 (1a, R = Me; 1b, R = H) containing olefinic groups with and without an internal methyl substitutent and the O-enyne HCî - CCH(OH)CMe2CH2OCH 2C(Me)=CH2 (1c) also with an internal methyl substituent on the olefinic group but with no aromatic group have been prepared. In the [Ru]Cl-induced ([Ru] = Cp(PPh)3Ru) reactions of 1a,c, the presence of the methyl group promotes cyclization reactions and their tandem cyclizations are further induced by MeOH. The reaction of 1a in CH2Cl2 gives the three products 2a-4a. Complex 2a, with a seven-membered thio ring bonded at Cβ of the vinylidene ligand, is formed via a C-C bond formation between two unsaturated groups in moderate yield. Complex 3a is formed via migration of PPh3 from the metal onto the terminal carbon of the alkynyl group followed by coordination of the S atom. The carbene complex 4a is formed by S addition to the internal carbon of the alkynyl group accompanied by migration of the allylic group from sulfur to the newly formed thiophene ring. Tandem cyclization of 1a in MeOH generates the organic product 8a via 2a. In the reaction, the vinylidene complex 7a, a formal methanol addition product of 2a, is also formed as a side product. Deprotonation of 7a gives the acetylide complex 9a. The reaction of 1c affords the vinylidene complex 2c in CH 2Cl2 via a similar cyclization process with no other side product. Deprotonation of 2c followed by allylation gave the disubstituted vinylidene complex 10c. Tandem cyclization of 1c in MeOH also gives the organic product 8c. In the reaction of [Ru]Cl with 1b containing no methyl group in the olefinic part, no C-C bond formation was observed. The reactions of [Ru]NCCH3+ with 1a,b each gave only 4a,b, respectively, with no side product. All of these reaction products are characterized by spectroscopic methods as well as elemental analysis. In addition, the structures of three complexes 5a, 9a, and 10c have been confirmed by X-ray diffraction analysis. © 2013 American Chemical Society.
SDGs
Type
journal article