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

Abstract

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.

Revisiting the Octadehydro[12]annulenes

“…Compounds 3 a – f were all bench stable for periods exceeding several weeks with no special storage requirements. Deprotection of the trimethylsilyl group to afford the bare alkyne (Step b) proceeded in good yield via established conditions, [32] and these deprotected diynes 4 a – f were typically used promptly without further purification, as they are somewhat unstable, even in solution. The Hay coupling to produce 12‐DHAs 1 a – f (Step c) was derived from literature precedent [26a] with several optimizations [33] .…”

Substituted Tetraethynylethylene–Tetravinylethylene Hybrids

“…Thus, Glaser homocouplings of TVEE ( 43 ), gem -DVDEE ( 32 and 33 ), and protected parent TEVE precursors gave buta-1,3-diyne-linked dehydro-dimers 69 – 72 . Alternatively, a 2-fold Sonogashira-type coupling of gem -DVDEE ( 33 ) with bis-carbonate 73 forged the DEBD-linked bis- gem -DVDEE structure 74 . The low isolated yields of system 72 are due to kinetic instability, which in the case of Glaser products improves both with increasing alkene content and alkene substitution (hence the increasing isolated yields of 69 , 71 , and 72 ).…”

A General Stereoselective Synthesis of [4]Dendralenes

“…The synthesis (conceptualized in the bottom section of Figure 1) leverages twofold couplings of propargylic diols, which have been previously used for the preparation of highly substituted dienes 13 and 2,3diethynyl-buta-1,3-dienes. 14 Thus, the first cross-coupling between a but-2-yn-1,4-yl biselectrophile 1 and an alkenylboronic ester 2 proceeds with 1,3propargyl to allenyl transposition to generate a substituted vinylallene 3. A second cross-coupling with another alkenylboronic ester 2 then ensues with 1,3-allylic transposition to generate the [4]dendralene 4.…”

“…Herein, we report the first general synthesis of [4]­dendralenes, as evidenced by the preparation of over 60 diversely functionalized molecules. The synthesis (conceptualized in the bottom section of Figure ) leverages twofold couplings of propargylic diols, which have been previously used for the preparation of highly substituted dienes and 2,3-diethynyl-buta-1,3-dienes …”