Toward 2-Thiophyne: Ketocarbene versus Hetaryne Intermediates from 2-(Trimethylsilyl)thiophen-3-yl Triflate.

The reaction of 2-(trimethylsilyl)thiophen-3-yl triflate with CsF in the presence of 2,3,4,5-tetraphenylcyclopentadienone affords 4,5,6,7-tetraphenylbenzo[b]thiophene, as it would be expected from the hypothesized generation and trapping of 2-thiophyne. However, a detailed experimental and computational study discards the intermediacy of this elusive 5-membered hetaryne. Instead, a complex mechanism involving the generation of an intermediate ketocarbene, which adds to the cyclopentadienone to give an isolable tricyclic intermediate, followed by thermal rearrangements, is proposed.

Building a 22-ring nanographene by combining in-solution and on-surface syntheses.

A nanographene formed by the fusion of 22 benzene rings has been prepared by combining an in-solution Pd-catalyzed cycloaddition reaction and on-surface Au-promoted cyclodehydrogenation. The structure and electronic properties of the resulting three-fold symmetric C66H24 molecule have been characterized by scanning probe microscopy with atomic resolution and corroborated by theoretical modelling.

1,7-Naphthodiyne: a new platform for the synthesis of novel, sterically congested PAHs.

The synthesis of an efficient precursor of the novel 1,7-naphthodiyne synthon is reported. Preliminary experiments demonstrate the usefulness of this platform for the synthesis of sterically congested polyarenes, such as helicenes and angularly fused acene derivatives. Furthermore, a novel intramolecular aryne trapping reaction is described.

Stereoselective tandem cascade furan cycloadditions.

Oligofurans linked by a rigid tether undergo tandem cycloaddition reactions with high stereoselectivity. The reaction of bisfurans with dimethyl acetylenedicarboxylate (DMAD) involves tandem [4 + 2]/[4 + 2] cycloadditions in a pincer mode. The reaction of oligofurans with arynes involves stereoselective tandem [4 + 2]/[4 + 2] cycloaddition reactions in a domino mode. The corresponding aryne adducts have been transformed into extended perylene derivatives by deoxygenation and aromatization with HCl/EtOH.

Aryne insertion into I-I σ-bonds.

A new protocol for the efficient synthesis of o-diiodoarenes has been developed. This method allows the synthesis of substituted and polycyclic o-diiodoarenes, which are difficult to obtain by classical methods. This diiodination process involves the formal insertion of arynes into the I-I σ-bond.

Highly selective insertion of arynes into a C(sp)-O(sp3) σ bond.

Arynes react with ethoxyacetylene to afford 2-ethoxyethynylaryl derivatives through a highly chemo- and regioselective formal insertion of the aryne into the C(sp)-O(sp(3)) bond of the alkyne. Computational studies suggest that the reaction does not proceed through a mechanism initiated by the nucleophilic addition of the oxygen atom to the aryne as previously proposed but by the addition of the triple bond of the alkyne to the aryne.

Tris(benzocyclobutadieno)triphenylene and its lower biphenylene homologues by palladium-catalyzed cyclizations of 2,3-didehydrobiphenylene.

[reaction: see text] The Pd-catalyzed cycloaddition of didehydrobiphenylenes 2a,b, generated from the corresponding 3-(trimethylsilyl)-2-biphenylenyl triflates with fluoride, furnishes the C3-symmetric trimers 1a,b in which the embedded triphenylene unit is distorted to increase the aromaticity of the central benzene ring. Cocyclization of 2a,b with dimethyl acetylenedicarboxylate provides the phenanthrene- and naphthalenecarboxylic ester analogues, depending on the catalyst used.

Dibenzo[a,o]phenanthro[3,4-s]pycene, a configurationally stable double helicene: synthesis and determination of its conformation by NMR and GIAO calculations.

[reaction: see text] A double helicene formed by a pentahelicene and a heptahelicene with two rings in common was obtained by palladium-catalyzed cyclotrimerization of 3,4-didehydrophenanthrene and was characterized conformationally by NMR and GIAO calculations.

Synthesis of Anisolylated Aspartyl and Glutamyl Tripeptides.

A process has been developed for transforming the beta-carboxyl of aspartate and the gamma-carboxyl of glutamate into anisolyl ketones. These ketones are occasional byproducts in peptide synthesis, resulting from deprotection or resin-removal processes in the presence of anisole as a scavenger. The ketone amino acids have been incorporated in a tripeptide by coupling with CBMIT. During peptide bond formation the keto group of the glutamyl residue required protection, which was provided as the ethylene dithioketal.