From propargylic biscarbonate to diaryl[n]dendralenes

A Pd-catalyzed highly selective three-component protocol for trisubstituted allenes

Herein we report the first example of a Pd-catalyzed highly selective three-component reaction of alkynyl-1,4-diol dicarbonates, organoboronic acids, and malonate anions for the efficient synthesis of trisubstituted 2,3-allenyl malonates not readily available by the known protocols. The reaction demonstrates an excellent regio- and chemo-selectivity for both the oxidative addition referring to the two C-O bonds and the subsequent coupling with the nucleophile with a remarkable functional group compatibility. A series of control experiments confirm a unique mechanism involving β-O elimination forming alka-1,2,3-triene and the subsequent insertion of its terminal C[double bond, length as m-dash]C bond into the Ar-Pd bond.

2-Butyne Biscarbonate as a "Bridge" in Rhodium(III)-Catalyzed [4 + 2] Cyclization and Diels-Alder Reaction

Described herein is the development of an unprecedented approach to construct multiple heterocycles with high selectivity through Rh(III)-catalyzed two- or three-component cyclization reaction from simple and readily available starting materials: N-methoxybenzamides, 2-butyne biscarbonate, and maleimides. This methodology provides an efficient strategy for the synthesis of diverse and complicated heterocycles in a one-pot manner and displays excellent features of extremely mild reaction conditions, easy operation, excellent regioselectivity, and good functional group compatibility.

A General Stereoselective Synthesis of [4]Dendralenes

The first general synthesis of branched tetraenes ([4]dendralenes) involves two or three steps from inexpensive, commodity chemicals. It involves an unprecedented variation on Suzuki-Miyaura cross-coupling, generating two new C-C bonds in a one-flask operation with control of diastereoselectivity. The broad scope of the method is established through the synthesis of more than 60 diversely substituted [4]dendralene molecules, along with substituted buta-1,3-dienes and other [n]dendralenes. [4]Dendralenes are demonstrated to be significantly more kinetically stable than their well-known [3]dendralene counterparts. The first stereoselective synthesis of these compounds is also reported, through the catalyst-controlled generation of both E- and Z-diastereomeric products from the same precursor. Novel, through-conjugated/cross-conjugated hybrid molecules are introduced. The first selective dienophile cycloadditions to substituted [4]dendralenes are reported, thus paving the way for applications in target-oriented synthesis.

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.