Unveiling the Chemistry and Synthetic Potential of Catalytic Cycloaddition Reaction of Allenes: A Review

Abstract

Allenes with two carbon–carbon double bonds belong to a unique class of unsaturated hydrocarbons. The central carbon atom of allene is sp hybridized and forms two σ-bonds and two π-bonds with two terminal sp2 hybridized carbon atoms. The chemistry of allenes has been well documented over the last decades. They are more reactive than alkenes due to higher strain and exhibit significant axial chirality, thus playing a vital role in asymmetric synthesis. Over a variety of organic transformations, allenes specifically undergo classical metal catalyzed cycloaddition reactions to obtain chemo-, regio- and stereoselective cycloadducts. This review briefly describes different types of annulations including [2+2], [2+2+1], [3+2], [2+2+2], [4+2], [5+2], [6+2] cycloadditions using titanium, cobalt, rhodium, nickel, palladium, platinum, gold and phosphine catalyzed reactions along with a mechanistic study of some highlighted protocols. The synthetic applications of these reactions towards the synthesis of natural products such as aristeromycin, ent-[3]-ladderanol, waihoensene(−)-vindoline and (+)-4-epi-vindoline have also been described.

Structural Characterization and Molecular Docking Screening of Most Potent 1,2,4-Triazine Sulfonamide Derivatives as Anti-Cancer Agents

“…Compound 5 has the lowest LUMO −2.50 eV energy, which suggests that it would be the best electron acceptor. Ionization potential and affinity are crucial properties that must be determined to predict the dynamic stability and chemical reactivity of molecules [21].…”

The Asymmetric Petasis Borono-Mannich Reaction: Insights on the Last 15 Years

“…This reaction approach was pointed out to be a traceless Petasis MCR, affording an allene product instead of the usual amine product. Due to the importance of allenes [49] as versatile building blocks in chemical transformations and their wide distribution in nature, the group of Schaus has looked into the enantioselective version of the traceless Petasis MCR using chiral diols as catalysts with high levels of asymmetric induction [45]. Two enantioselective procedures were reported to access the chiral allenes 42 and 43 from achiral Studies considering the use of sulfonylhydrazines 41 and allyl boronates in the traceless Petasis MCR were developed by the group of Schaus, extending the scope of the reaction to the use of enals as the aldehyde component, catalyzed by chiral biphenols.…”