Tandem Cyclization of Enynes Containing a Thioether or Ether Linkage via Ruthenium Allenylidene and Vinylidene Complexes

The two aromatic S-enynes HCCCH­(OH)­(C₆H₄)­SCH₂C­(R)CH₂ (<b>1a</b>, R = Me; <b>1b</b>, R = H) containing olefinic groups with and without an internal methyl substitutent and the O-enyne HCCCH­(OH)­CMe₂CH₂OCH₂C­(Me)CH₂ (<b>1c</b>) 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 <b>1a</b>,<b>c</b>, the presence of the methyl group promotes cyclization reactions and their tandem cyclizations are further induced by MeOH. The reaction of <b>1a</b> in CH₂Cl₂ gives the three products <b>2a</b>–<b>4a</b>. Complex <b>2a</b>, with a seven-membered thio ring bonded at C_β of the vinylidene ligand, is formed via a C–C bond formation between two unsaturated groups in moderate yield. Complex <b>3a</b> 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 <b>4a</b> 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 <b>1a</b> in MeOH generates the organic product <b>8a</b> via <b>2a</b>. In the reaction, the vinylidene complex <b>7a</b>, a formal methanol addition product of <b>2a</b>, is also formed as a side product. Deprotonation of <b>7a</b> gives the acetylide complex <b>9a</b>. The reaction of <b>1c</b> affords the vinylidene complex <b>2c</b> in CH₂Cl₂ via a similar cyclization process with no other side product. Deprotonation of <b>2c</b> followed by allylation gave the disubstituted vinylidene complex <b>10c</b>. Tandem cyclization of <b>1c</b> in MeOH also gives the organic product <b>8c</b>. In the reaction of [Ru]Cl with <b>1b</b> containing no methyl group in the olefinic part, no C–C bond formation was observed. The reactions of [Ru]­NCCH₃⁺ with <b>1a</b>,<b>b</b> each gave only <b>4a</b>,<b>b</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 <b>5a</b>, <b>9a</b>, and <b>10c</b> have been confirmed by X-ray diffraction analysis

Tandem Cyclization of Enynes Containing a Thioether or Ether Linkage via Ruthenium Allenylidene and Vinylidene Complexes

The two aromatic S-enynes HCCCH­(OH)­(C₆H₄)­SCH₂C­(R)CH₂ (<b>1a</b>, R = Me; <b>1b</b>, R = H) containing olefinic groups with and without an internal methyl substitutent and the O-enyne HCCCH­(OH)­CMe₂CH₂OCH₂C­(Me)CH₂ (<b>1c</b>) 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 <b>1a</b>,<b>c</b>, the presence of the methyl group promotes cyclization reactions and their tandem cyclizations are further induced by MeOH. The reaction of <b>1a</b> in CH₂Cl₂ gives the three products <b>2a</b>–<b>4a</b>. Complex <b>2a</b>, with a seven-membered thio ring bonded at C_β of the vinylidene ligand, is formed via a C–C bond formation between two unsaturated groups in moderate yield. Complex <b>3a</b> 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 <b>4a</b> 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 <b>1a</b> in MeOH generates the organic product <b>8a</b> via <b>2a</b>. In the reaction, the vinylidene complex <b>7a</b>, a formal methanol addition product of <b>2a</b>, is also formed as a side product. Deprotonation of <b>7a</b> gives the acetylide complex <b>9a</b>. The reaction of <b>1c</b> affords the vinylidene complex <b>2c</b> in CH₂Cl₂ via a similar cyclization process with no other side product. Deprotonation of <b>2c</b> followed by allylation gave the disubstituted vinylidene complex <b>10c</b>. Tandem cyclization of <b>1c</b> in MeOH also gives the organic product <b>8c</b>. In the reaction of [Ru]Cl with <b>1b</b> containing no methyl group in the olefinic part, no C–C bond formation was observed. The reactions of [Ru]­NCCH₃⁺ with <b>1a</b>,<b>b</b> each gave only <b>4a</b>,<b>b</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 <b>5a</b>, <b>9a</b>, and <b>10c</b> have been confirmed by X-ray diffraction analysis

Domino Cyclization of 1,<i>n</i>‑Enynes (<i>n</i> = 7, 8, 9) Giving Derivatives of Pyrane, Chromene, Fluorene, Phenanthrene and Dibenzo[7]annulene by Ruthenium Complexes

Cyclization of the ether enyne <b>1</b> catalyzed by [Ru]­NCCH₃⁺ ([Ru] = Cp­(PPh₃)₂Ru) in CHCl₃ generates a diastereomeric mixture of the substituted tetrahydropyran <b>11</b>. Presumably, formation of an allenylidene complex is followed by a cyclization by nucleophilic addition of the olefinic group to Cγ of the ligand giving a boat-like six-membered ring. The diastereoselectivity is controlled by the 1,3-diaxial interaction. The vinylidene complex <b>7</b>, a precursor of <b>11</b>, is obtained from <b>1</b> and [Ru]­Cl. In a mixture of MeOH/CHCl₃, the domino cyclization of <b>1</b> further affords <b>14a</b>, a chromene product catalytically. The second cyclization proceeds via nucleophilic addition of the resulting olefinic unit to Cα of <b>7</b>. But the ether enyne <b>3</b> with a cyclopentyl ring on the olefinic unit undergoes only single cyclization due to steric effect. The propargyl alcohol and the two terminal methyl groups on the olefinic unit shape the cyclization. Thus, similar all-carbon 1,<i>n</i>-enynes (<i>n</i> = 7, 8, 9) <b>4</b>–<b>6</b> each with an aromatic linker undergo direct domino cyclization catalyzed by [Ru]­NCCH₃⁺, to give derivatives of tricyclic fluorene, phenanthrene and dibenzo[7]­annulene, respectively, with no intermediate observed

Domino Cyclization of 1,<i>n</i>‑Enynes (<i>n</i> = 7, 8, 9) Giving Derivatives of Pyrane, Chromene, Fluorene, Phenanthrene and Dibenzo[7]annulene by Ruthenium Complexes

Cyclization of the ether enyne <b>1</b> catalyzed by [Ru]­NCCH₃⁺ ([Ru] = Cp­(PPh₃)₂Ru) in CHCl₃ generates a diastereomeric mixture of the substituted tetrahydropyran <b>11</b>. Presumably, formation of an allenylidene complex is followed by a cyclization by nucleophilic addition of the olefinic group to Cγ of the ligand giving a boat-like six-membered ring. The diastereoselectivity is controlled by the 1,3-diaxial interaction. The vinylidene complex <b>7</b>, a precursor of <b>11</b>, is obtained from <b>1</b> and [Ru]­Cl. In a mixture of MeOH/CHCl₃, the domino cyclization of <b>1</b> further affords <b>14a</b>, a chromene product catalytically. The second cyclization proceeds via nucleophilic addition of the resulting olefinic unit to Cα of <b>7</b>. But the ether enyne <b>3</b> with a cyclopentyl ring on the olefinic unit undergoes only single cyclization due to steric effect. The propargyl alcohol and the two terminal methyl groups on the olefinic unit shape the cyclization. Thus, similar all-carbon 1,<i>n</i>-enynes (<i>n</i> = 7, 8, 9) <b>4</b>–<b>6</b> each with an aromatic linker undergo direct domino cyclization catalyzed by [Ru]­NCCH₃⁺, to give derivatives of tricyclic fluorene, phenanthrene and dibenzo[7]­annulene, respectively, with no intermediate observed