Dihydrobiphenylenes through Ruthenium‐Catalyzed [2+2+2] Cycloadditions of ortho‐Alkenylarylacetylenes with Alkynes

Abstract

A new synthetic route to dihydrobiphenylenes has been developed. The process involves a mild Ru(II) -catalyzed [2+2+2] dimerization of ortho-alkenylarylacetylenes or its more versatile variant, the Ru-catalyzed [2+2+2] cycloaddition of ortho-ethynylstyrenes with alkynes. Mechanistic aspects of this [2+2+2] cycloaddition are discussed.

Ruthenium‐Catalyzed Cycloisomerization of 2‐Alkynylstyrenes via 1,2‐Carbon Migration That Leads to Substituted Naphthalenes

“…Initially, we investigated the impact of the structure of the styrene moiety in 2‐(phenylethynyl)styrene derivatives ( 1 ) on the carbocyclization using [CpRuCl(dppe)]/NaBAr F 4 ⋅2 H 2 O (Ar F =3,5‐(CF 3 ) 2 C 6 H 3 ) as the catalytic system, which was found to be highly active in the previous studies . When a mixture of 2‐(phenylethynyl)styrene ( 1 a ), [CpRuCl(dppe)] (10 mol %), and NaBAr F 4 ⋅2 H 2 O (12 mol %) was stirred at 130 °C for 2 h in xylene, the desired 1,2‐aryl migration product, 1‐phenylnaphthalene ( 2 a ), was formed in 74 % yield (Table ).…”

“…[15] Initially,w ei nvestigated the impact of the structure of the styrene moiety in 2-(phenylethynyl)styrene derivatives (1)o n the carbocyclization using [CpRuCl(dppe)]/NaBAr F 4 ·2 H 2 O( Ar F = 3,5-(CF 3 ) 2 C 6 H 3 )a st he catalytic system,w hich was found to be highly active in the previouss tudies. [14,16] When am ixture of 2-(phenylethynyl)styrene (1a), [CpRuCl(dppe)] (10 mol %), and NaBAr F 4 ·2 H 2 O( 12 mol %) was stirred at 130 8Cf or 2hin xylene, the desired 1,2-aryl migration product, 1-phenylnaphthalene (2a), was formed in 74 %y ield ( Table 1). Alkyne 1b with an amethylstyryl group was more reactive than 1a and converted into the corresponding 1,4-disubstituted naphthalene 2b in 91 %y ield after 1h in the presence of as maller amount (6 mol %) of [CpRuCl(dppe)].T his result can be rationalized by postulating that 1b adopts an appropriate conformation for the cyclizationu pon the introductiono ft he methyl group.…”

Assembly of a Benzo‐Fused Bridged Ketone Scaffold from 1,5,10‐Enediynes through One‐Pot Ruthenium‐Catalyzed Cyclization/Iodine‐Mediated Oxidative Ring Expansion

“…An eutral Ru complex, [Cp*RuCl(cod)] (Cp* = h 5 -C 5 Me 5 ,cod = 1,5-cyclooctadiene), was found to be an optimal catalyst for diverse [2+ +2+ +2] cycloaddition reactions of diynes. [8] Following this report, we used the same Ru catalyst for the intramolecular reaction of 1a (Scheme 1). [7] On the other hand, Saµ and coworkers observed ap rototypical intermolecular cyclodimerization of o-alkynyl styrenes with ac ationic Ru complex, [Cp*Ru(MeCN) 3 ]PF 6 ,asthe catalyst.…”

“…[6] However,w er ecently found that [Cp*RuCl(cod)] catalyzed the cycloisomerization of 1a to afford the indenylidene cyclic ether (Z)-3a rather than its [2+ +2+ +2] cyclization. [8] Notably,asignificant amount of (Z)-3a was still produced under these conditions with the cationic catalyst, thus indicating that the intramolecular setting is favorable for cycloisomerization. [8] Following this report, we used the same Ru catalyst for the intramolecular reaction of 1a (Scheme 1).…”

“…[7] On the other hand, Saµ and coworkers observed ap rototypical intermolecular cyclodimerization of o-alkynyl styrenes with ac ationic Ru complex, [Cp*Ru(MeCN) 3 ]PF 6 ,asthe catalyst. [8] Following this report, we used the same Ru catalyst for the intramolecular reaction of 1a (Scheme 1). Thet reatment of 1a with [Cp*Ru-(MeCN) 3 ]PF 6 (10 mol %) in acetonitrile at room temperature for 2hafforded an inseparable mixture of the desired product 2a and (Z)-3a in 35 and 59 %y ield, respectively,a s determined by 1 HNMR spectroscopy.A lthough 2a was unstable and could not be separated from (Z)-3a, 2a was identified as adihydrobiphenylene derivative by comparison with previously reported cyclodimerization products.…”