Development of an Allenyne-Alkyne [4+2] Cycloaddition and its Application to Total Synthesis of Selaginpulvilin A.

A new [4+2] cycloaddition of allenyne-alkyne is developed. The reaction is believed to proceed with forming an α,3-dehydrotoluene intermediate. This species behaves as a σπ-diradical to react with a hydrogen atom donor, whereas it displays a zwitterionic reactivity toward weak nucleophiles.

Ruthenabenzene: A Robust Precatalyst.

Metallaaromatics constitute a unique class of aromatic compounds where one or more transition metal elements are incorporated into the aromatic system, the parent of which is metallabenzene. One of the main concerns about metallabenzenes generally deals with the structural characterization related to their relative aromaticity compared to the carbon archetype. Transition metal-containing metallabenzenes are also implicated in certain catalytic processes such as alkyne metathesis polymerization; however, these transition metal-based metallaaromatic compounds have not been developed as a catalyst.

Alder-ene reactions driven by high steric strain and bond angle distortion to form benzocyclobutenes.

A unique aryne-based Alder-ene reaction to form benzocyclobutene is described. In this process, the thermodynamic barrier to form a four-membered ring is compensated by the relief of the strain energy of an aryne intermediate. On the other hand, the driving force to overcome the high kinetic barrier is provided by the gearing effect of the bulky substituent at the -position of the ene-donor alkene.

Reactivity and Selectivity in the Intermolecular Alder-Ene Reactions of Arynes with Functionalized Alkenes.

The reactivity and selectivity of functionalized alkenes in intermolecular Alder-ene reactions with arynes is described. The arynes generated from bis-1,3-diynes react with various trisubstituted and 1,1-disubstituted alkenes containing hydroxyl, amino, halo, carboxyl, boronate, and 1,3-dienyl functionalities, providing product distributions with varying degrees of selectivity between Alder-ene and addition reactions. The geometry of alkenes is another important factor for the reactivity of di- and trisubstituted alkenes where the allylic hydrogen of cis-disposed alkenyl system is reactive, which is the opposite reactivity compared to the corresponding intramolecular reaction.