Synthesis of Enediynes by Diels-Alder Addition

Regio- and stereocontrolled synthesis of borylated E-enynes, Z-enediynes and derivatives from alkenyl-1,2-bis-(boronates)

An efficient stereo-controlled synthesis of enyne and enediyne derivatives, via sequential Suzuki-Miyaura coupling reactions from easily prepared 1-alkene-1,2-diboronic esters and alkynyl bromides, is reported. The resulting enyne boronic esters were subjected to Borono-Mannich and Suzuki coupling reactions independently to obtain α,β-unsaturated aminoester and tri-substituted olefin derivatives, respectively. Additionally, divergent syntheses of triazole and cyclopropylboronate derivatives are also reported.

Synthesis and Properties of 2,3-Diethynyl-1,3-Butadienes

The first general preparative access to compounds of the 2,3-diethynyl-1,3-butadiene (DEBD) class is reported. The synthesis involves a one-pot, twofold Sonogashira-type, Pd⁰ -catalyzed coupling of two terminal alkynes and a carbonate derivative of a 2-butyne-1,4-diol. The synthesis is broad in scope and members of this structural family are kinetically stable enough to be handled using standard laboratory techniques at ambient temperature. They decompose primarily through heat-promoted cyclodimerizations, which are impeded by alkyl substitution and accelerated by aryl or alkenyl substitution. An iterative sequence of these unprecedented Sonogashira-type couplings generates a new type of expanded dendralene. A suitably substituted DEBD carrying two terminal alkyne groups undergoes Glaser-Eglinton cyclo-oligomerization to produce a new class of expanded radialenes, which are chiral due to restricted rotation about their 1,3-butadiene units. The structural features giving rise to atropisomerism in these compounds are distinct from those reported previously.

Highly Selective Synthesis of cis-Enediynes on a Ag(111) Surface

Cis-enediyne-type compounds have received much attention as potent antitumor antibiotics. The conventional synthesis of cis-enediynes in solution typically involves multiple steps and various side reactions. For the first time, selective one-step synthesis of cis-enediyne from a single reactant is reported on a Ag(111) surface with a yield up to 90 %. High selectivity for the formation of cis-enediyne originates from the steric effect posed by weak intermolecular interactions, which protect the cis-enediyne from further reaction. A series of comparative experiments and DFT-based transition-state calculations support the findings. The described synthetic approach for directing reaction pathways on-surface may illuminate potential syntheses of other unstable organic compounds.

Discovery and Computational Rationalization of Diminishing Alternation in [n]Dendralenes

The [n]dendralenes are a family of acyclic hydrocarbons which, by virtue of their ability to rapidly generate structural complexity, have attracted significant recent synthetic attention. [3]Dendralene through [8]dendralene have been previously prepared but no higher member of the family has been reported to date. Here, we describe the first chemical syntheses of the "higher" dendralenes, [9]dendralene through [12]dendralene. We also report a detailed investigation into the spectroscopic properties and chemical reactivity of the complete family of fundamental hydrocarbons, [3]dendralene to [12]dendralene. These studies reveal the first case of diminishing alternation in behavior in a series of related structures. We also report a comprehensive series of computational studies, which trace this dampening oscillatory effect in both spectroscopic measurements and chemical reactivity to conformational preferences.

Stereoselective Iterative Convergent Synthesis of Z-Oligodiacetylenes from Propargylic Dithioacetals

A series of (t)Bu-substituted Z-oligodiacetylenes (Z-ODAs) are synthesized from the reactions of allenyl/propargylic zinc reagents, obtained from the corresponding propargylic dithiolanes and BuLi, with dithiolane-substituted propargylic aldehydes followed by stereospecific elimination of β-thioalkoxy alcohols under Mitsunobu conditions. The stereochemical assignments are based on NOE experiments. The X-ray structure of the hexamer further supports the Z configuration for each of the double bonds in these ODAs. The photophysical properties of these Z-ODAs have been examined and are compared with known related E- and Z-ODAs with different substituents.

Synthesis of Bicyclic Enediynes from Bis[phenyl[(trifluoromethanesulfonyl)oxy]iodo]acetylene: A Tandem Diels-Alder/Palladium(II)- and Copper(I)-Cocatalyzed Cross-Coupling Approach

The reaction of bicycloalkenylbis(phenyliodonium) triflates 1a or b (available via the Diels-Alder reaction of bis[phenyl[(trifluoromethanesulfonyl)oxy]iodo]acetylene with cyclopentadiene or furan, respectively) with alkynylstannanes 2a-g at room temperature in DMF in the presence of catalytic amounts of trans-benzyl(chloro)bis(triphenylphosphine)palladium(II) and copper(I) iodide proceeds smoothly and with selectivity to afford good to excellent yields of bicyclic enediynes 3a-k.