Reactions of Aromatic S‐ and O‐Enynes with Two Methyl Substituents on the Olefinic Unit Assisted by a Ruthenium Complex: Tandem Cyclization and Product Selectivity. Issue 2 (21st November 2013)

• Record Type: Journal Article
• Authors: Feng, Yi‐Jhen; Lai, Ying‐Hsuan; Lin, Ying‐Chih; Huang, Shou‐Ling; Liu, Yi‐Hung
• Is Part Of: Chemistry, an Asian journal. Volume 9:Issue 2(2014:Feb.)
• Page Start: 602
• Page End: 611
• Publication Date: 2013-11-21
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1002/asia.201301264
• Languages: English
• ISSNs: 1861-4728

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>Ruthenium‐assisted cyclizations of two enynes, HC≡CCH(OH)(C<sub>6</sub>H<sub>4</sub>)XCH<sub>2</sub>CHCMe<sub>2</sub> (X=S (<bold>1 a</bold>), O (<bold>1 b</bold>)), each of which contains two terminal methyl substituents on the olefinic parts, are explored. The reaction of <bold>1 a</bold> in CH<sub>2</sub>Cl<sub>2</sub> gives the vinylidene complex <bold>2 a</bold> from the first cyclization and two side products, <bold>3 a</bold> and the carbene complex <bold>4 a</bold> with a benzothiophene ligand. The same reaction in the presence of HBF<sub>4</sub> affords <bold>4 a</bold> exclusively. Air oxidation of <bold>4 a</bold> in the presence of Et<sub>3</sub>N readily gives an aldehyde product. In MeOH, tandem cyclizations of <bold>1 a</bold> generate a mixture of the benzothiochromene compound <bold>10 a</bold> and the carbene complex <bold>7 a</bold> also with a benzothiochromene ligand. First, cyclization of <bold>1 b</bold> likewise proceeds in CH<sub>2</sub>Cl<sub>2</sub> to give <bold>2 b</bold>. Tandem cyclization of <bold>1 b</bold> in MeOH yields comparable products <bold>10 b</bold> and <bold>7 b</bold> with benzochromene moieties, yet with no other side product. The reaction of [Ru]Cl with HC≡CCH(OH)(C<sub>6</sub>H<sub>4</sub>)SCH<sub>2</sub>CHCH<sub>2</sub> (<bold>1 c</bold>), which contains no methyl substituent in the olefinic part, in MeOH gives the carbene complex <bold>15 c</bold> with an unsubstituted thiochromene by means of a CS bond formation. Structures of <bold>3 a</bold> and <bold>15 c</bold> are confirmed by X‐ray diffraction analysis. The presence of methyl groups of enynes <bold>1 a</bold> and <bold>1 b</bold> promotes sequential cyclization reactions that involve CC bond formation through carbocationic species.</p> </abstract>