Novel [4 + 2] cycloaddition reactions of alkyne and enyne key-units: Direct access to bicyclic aromatic and heteroaromatic products. A theoretical mechanistic study

Computational Study of a Model System of Enzyme-Mediated [4+2] Cycloaddition Reaction

“…Reaction ( a ) was investigated in several previous studies (see refs. [ 8 , 9 , 10 , 11 , 12 , 13 , 39 , 40 , 42 , 43 , 44 , 45 , 46 , 71 , 72 , 73 , 74 , 75 , 76 , 77 , 78 , 79 , 80 , 81 , 82 ]) and the calculations here are provided for comparative purpose.…”

“…Rapid development of Diels-Alder [4+2] cycloaddition chemistry has explored new opportunities and fascinating applications leading to elaboration of efficient practical procedures and resulting in high product yields. An amazing feature revealed for cycloaddition reactions is a wide substrate scope and high tolerance to various functional groups present in the substrate [ 1 , 2 , 3 , 4 , 8 , 9 , 10 , 11 , 12 , 13 ]. Ultimately, this approach can provide an efficient chemical methodology to access a diverse range of cyclic products of key-importance.…”

“…However, the stumbling block in cycloaddition chemistry is the development of a new generation of catalysts to achieve high stereoselectivity and enantioselectivity under mild conditions (preferably at room temperature). Since enzymatic catalysis has not yet been employed in the area, many potentially very useful cycloaddition reactions are currently carried out at high temperatures of 100–200°C and require additional chemical reagents to speed up the transformation (to be removed as wastes at the product purification step) [ 8 , 9 , 10 , 11 , 12 , 13 ].…”

Nickel: The “Spirited Horse” of Transition Metal Catalysis

“…The high affinity of nickel complexes to unsaturated organic molecules led to the discovery of numerous fascinating transformations involving alkynes, alkenes, and dienes, with several bright examples appearing in ongoing development. − , Our group has developed atom-economic addition reactions of alkynes, in which the superior catalytic properties of the Ni catalyst were employed for selective carbon–heteroatom bond formation …”

Tandem [4 + 2]/[2 + 2] cycloaddition of o-carboryne with enynes: facile construction of carborane-fused tricyclics

“…At first, in situ generated o -carboryne A by reaction of 1 with LiHMDS, reacts with conjugated enyne 2 to form highly reactive carborane-fused 1,2-cyclohexadiene B via [4 + 2] cycloaddition. 20 Two molecules of cyclic allenes B undergo a stepwise [2 + 2] cycloaddition via a singlet bis-allyl diradical C intermediate, 21 affording the desired carborane-fused tricyclo[6.4.0.0 2,7 ]dodeca-2,12-diene 3 . This proposed mechanism is supported by DFT calculations (see ESI † for details).…”