Commercially available ruthenium catalyst, Cp*RuCl(COD), was found to be active in catalyzing Bis-Homo-Diels-Alder [2+2+2] cycloaddition reactions between 1,5-cyclooctadiene and various alkynes giving moderate to good yields (35%–92%). The presence of electron donating groups, especially hydroxyl groups, greatly enhanced the reactivity of the alkyne moiety in the cycloaddition. The reaction was also found to be successful even in the presence of bulky substituents on the alkynes.

Background: Transition metal-catalyzed reactions of alkynyl halides are a versatile means of synthesizing a wide array of products. Their use is of particular interest in cycloaddition reactions and in constructing new carbon-carbon and carbon-heteroatom bonds. Transition metal-catalyzed reactions of alkynyl halides have successfully been used in [4+2], [2+2], [2+2+2] and [3+2] cycloaddition reactions. Many carbon-carbon coupling reactions take advantage of metal-catalyzed reactions of alkynyl halides, including Cadiot-Chodkiewicz, Suzuki-Miyaura, Stille, Kumada-Corriu and Inverse Sonogashira reactions. All the methods of constructing carbon-nitrogen, carbon-oxygen, carbon-phosphorus, carbon-sulfur, carbon-silicon, carbon-selenium and carbon-tellurium bonds employed alkynyl halides. Objective: The purpose of this review is to highlight and summarize research conducted in transition metalcatalyzed reactions of alkynyl halides in recent years. The focus will be placed on cycloaddition and coupling reactions, and their scope and applicability to the synthesis of biologically important and industrially relevant compounds will be discussed. Conclusion: It can be seen from the review that the work done on this topic has employed the use of many different transition metal catalysts to perform various cycloadditions, cyclizations, and couplings using alkynyl halides. The reactions involving alkynyl halides were efficient in generating both carbon-carbon and carbonheteroatom bonds. Proposed mechanisms were included to support the understanding of such reactions. Many of these reactions face retention of the halide moiety, allowing additional functionalization of the products, with some new products being inaccessible using their standard alkyne counterparts.

The ruthenium-catalyzed [2+2+2] bis-homo-Diels–Alder cycloaddition between 1,5-cyclooctadiene and alkynyl phosphonates was investigated. Various alkynyl phosphonate moieties were found to be compatible with the cycloaddition to give the tricyclo[4.2.2.02,5]dec-7-ene tricyclic compounds in yields of 46–97%.

Objective: The ruthenium-catalyzed Bis-Homo-Diels-Alder cycloaddition between 1,5- cyclooctadiene and alkynes was explored, and the use of commercially available cationic catalysts was investigated. It was noted that [CpRu(CH3CN)3]PF6 was effective at catalyzing this cycloaddition and yields of the desired tricyclo[4.2.2.02,5]dec-7-ene adduct ranging from 13 to 83% were achieved using this cationic catalyst. Several cycloadducts that were previously unobtainable with the use of the neutral (Cp*RuCl(COD) catalysts were also successfully made using [CpRu(CH3CN)3]PF6 albeit in low yields. Methods: Commercially available, and previously synthesized alkynes were combined with 1,5-cyclooctadiene and treated with a ruthenium catalyst within a glovebox. The reaction mixture was stirred for 72h at temperatures ranging from 25 to 70oC. The desired cycloadduct was then isolated using flash column chromatography and analyzed and characterized using NMR, IR and MS. Results: Several previously unattainable adducts were synthesized using the cationic [CpRu(CH3CN)3]PF6. When this catalyst was compared to the neutral Cp*RuCl(COD) greater yields were observed. Conclusion: The present study describes an improved method for the formation of the tricyclo[4.2.2.02,5]dec-7- ene framework using a commercially available cationic ruthenium catalyst. It was noted that the use of [CpRu(CH3CN)3]PF6 led to improved yields when compared to Cp*RuCl(COD).