Cobalt-Catalyzed Divergent Cycloadditions of Alkynes with Conjugated Dienes Yielding 3-Vinylcyclobutenes, Bicyclo[3.1.0]hexenes, and Cyclohexa-1,4-dienes

A traditional cobalt catalyst system still contains undiscovered reactivity. Depending on the tertiary phosphines and substrates used, the catalytic system using CoBr₂/tertiary phosphine/Zn/ZnI₂ catalyzes divergent cycloadditions of internal alkynes with conjugated dienes, yielding 3-alkenylcyclobut-1-enes, bicyclo[3.1.0]hexenes, and cyclohexa-1,4-dienes. A [CoBr₂(PPh₃)₂]/Zn/ZnI₂-catalyzed reaction of 3-hexyne (1a) with 1-(4-methoxyphenyl)butadiene (2a) at room temperature in CH₂Cl₂ exclusively produces a [2 + 2] cycloaddition product (E)-2-(2,3-diethylcyclobut-2-ene-1-yl)vinyl-4-methoxybenzene (3aa). When [CoBr₂(dppp)]/Zn/ZnI₂ is used as a catalyst, a bicyclic compound 6-(4-methoxyphenyl)-2,3-diethylbicyclo[3.1.0]hex-2-ene (4aa) is dominantly formed in a 77% yield. The CoBr₂/dppe/Zn/ZnI₂ system can undergo a [2 + 4] cycloaddition to yield 3-(4-anisyl)-1,2-diethylcyclohexa-1,4-diene (5aa) as the dominant product in 38% yield. The bite angles of the ligands used contribute significantly to this catalytic diversity.

Synthesis and reactivity of alkynyl boron compounds

Over the last century, there have been considerable developments in organoboron chemistry due to the stability, non-toxicity, and easy commercial availability of various boronic esters. Several organoboron reagents have emerged and play an increasingly important role in everyday organic synthesis. Among them, alkynyl boron compounds have attracted significant attention due to their easy synthesis and diverse reactivity. In this review, we summarize the advancement of research on alkynyl boron compounds, highlighting their importance in the synthesis of valuable compounds.

New strategy for synthesising conjugated hexatrienylferrocenes via cross-dimerisation

A new strategy giving hexatrienylferrocenes.

Synthesis of Symmetrical and Nonsymmetrical Polyenes by Iterative and Bidirectional Palladium-Catalyzed Cross-Coupling Reactions

Bifunctional unsaturated reagents designed to undergo palladium-catalyzed cross-coupling reactions with complementary polyenyl connective fragments are highly useful for the undoubtedly challenging synthesis of polyenes. The current toolkit of building blocks for the bidirectional formation of Csp² -Csp² single bonds of polyenes includes homo-bisfunctionalized reagents with equal or unequal reactivity (due to steric and/or electronic factors), and hetero-bisfunctionalized counterparts containing either two different nucleophiles, two electrophiles or one of these functionalities and a latent nucleophile that can be unmasked when desired. The combination of these bifunctional linchpin reagents using tactics that modulate the reactivity of each terminus in order to achieve the required connection have streamlined the synthesis of polyenes of great complexity using (iterative) cross-coupling methods for Csp² -Csp² bond formation. Reaction conditions for the Pd-catalyzed cross-coupling reactions are mild and functional-group-tolerant, and therefore these protocols allow to construct the polyene structures using shorter unsaturated reactants with the desired geometries, since in general the products preserve the stereochemical information of the connected cross-coupling partners.

An insight into regioselectivity in the transformation through a ruthenacycle

Ru(0)-Catalysed cross-dimerisation of unsymmetrical internal alkynes with conjugated dienes yields two conjugated trienes depending on the regioselectivity. The regioselectivity is dominantly controlled by the induction effect of the substituents.