Tsun Cheng Wu

Palladium-catalyzed formation of highly substituted naphthalenes from arene and alkyne hydrocarbons

Several highly substituted naphthalenes 3 have been synthesized in a one-pot reaction by treatment of arenes 1 with alkynes 2 in the presence of palladium acetate and silver acetate. In this Pd-catalyzed protocol, an arene provides a benzo source for the construction of a naphthalene core through twofold aryl C-H bond activation. Reaction of triphenylphosphine with diphenylethyne (2 a) under the catalysis of Pd(IV) complexes produced 1,2,3,4-tetraphenylnaphthalene (3 ba) in 62 % yield. Here, triphenylphosphine undergoes one aryl C-P bond cleavage and one aryl C-H bond activation to serve as a benzo moiety. Crystal structures of cycloadducts 3 ea, 3 ga, and 3 ac have been analyzed. The twisted naphthalenes arise not only from the overcrowded substituents but also from the contribution of the CH(3)-pi interaction.

Synthesis and structural analysis of a highly curved buckybowl containing corannulene and sumanene fragments.

Buckybowls 7, 9, and 10 were prepared from benzo[k]fluoranthene 6 and fluoranthene 8 using straightforward procedures involving key palladium-catalyzed cyclization reactions. The structures of bowl-shaped molecules 7 and 10 were determined by using X-ray crystallographic methods. The observed p-orbital axis vector (POAV) angle of 7 was found to be 12.8°.

Synthesis, Structures, and Physical Properties of Benzo[k]fluoranthene-Based Linear Acenes†

This work describes the syntheses, crystal structures, photophysical properties, and electro-chemical analyses of benzo[k]fluoranthene-based linear acenes, together with ab initio density functional theory computations on them. The molecules were prepared in generally moderate to good yields through Pd-catalyzed cycloadditions between 1,8-diethynylnaphthalene derivatives and aryl iodides. This protocol is simpler and more efficient than conventional methods. The scope and limitations of this reaction were examined. The structures of compounds 4hb, 15ac, 17ab, 19ac, and 24je were determined by X-ray analysis; they are either bent or twisted, rather than planar. The photophysical and electrochemical properties of these cycloadducts were also investigated and compared with computational predictions based on density functional theory.

Highly Curved Bowl‐Shaped Fragments of Fullerenes: Synthesis, Structural Analysis, and Physical Properties

Highly curved buckybowls 3, 4, and 5 were synthesized from planar precursors, fluoranthenes 8, benzo[k]fluoranthenes 10 and naphtho[1,2-k]-cyclopenta[cd]fluoranthenes 12, respectively, using straightforward palladium-catalyzed cyclization reactions. These fluoranthene-based starting materials were easily prepared from 1,8-bis(arylethynyl)naphthalenes 6. Both buckybowls 3 and 4 are fragments of C60 , whereas 5 is a unique subunit of C70 . The curved structures were identified by X-ray crystallography, and they are deep bowls. The maximum π-orbital axis vector (POAV) pyramidalization angle in both 3 and 4 is 12.8°. Such a high curvature is very rarely obtained. Buckybowls 5 are less curved than the others because they have a lower density of five-membered rings, analogous to the tube portion of C70 . Cyclopentaannulation increases the bowl depths of 3 and 4, but not the maximum POAV pyramidalization angle. Among the eight buckybowls studied herein, five form polar crystals. The bowl-to-bowl inversion dynamics of these buckybowls can be classified into two types; one has a planar transition structure, whereas the other has an S-shaped transition structure. A larger longitudinal length of these buckybowls corresponds to a stronger preference for the latter. The photophysical properties of these buckybowls were examined and compared with those of C60 and C70 . Buckybowls 5 have absorption bands at wavelengths greater than 450u2005nm, which are similar to those of C70 . The chiral resolution of the mono-substituted buckybowl 4u2009ac was also studied by using HPLC with a chiral column.

Palladium-catalyzed cycloisomerizations of diarylacetylenes: synthesis, structures, and physical properties of highly substituted naphthalenes and 8,8 a-dihydrocyclopenta[a]indenes

Depending on the electronic properties of their substituents, the major products generated by palladium-catalyzed cycloisomerizations of diarylalkynes are either highly substituted 8,8a-dihydrocyclopenta[a]indenes 3 or naphthalenes 4. The structures of these compounds were verified by X-ray crystallographic analysis. Many functional groups tolerated the reaction conditions evaluated in this study. The isotope-labeled experiments indicated that added water has a critical role in forming both classes of compounds. The photophysical and electrochemical properties of cycloadducts 3 and their analogues were systematically studied and compared with computational predictions based on density functional theory. Dihydrocyclopenta[a]indenes 3 in either solid or liquid form display strong luminescence, whereas cyclopenta[a]indene 11u2009j is practically nonfluorescent. The functional groups directly attached to the backbone of compound 3 significantly influenced physical properties. The steric effect arising from the aryl substituents caused different luminescence phenomena, including aggregation-induced and -enhanced emission.

Synthetic and structural considerations on highly curved bowl-shaped fragments of fullerenes

Abstract Numerous highly curved fragments of C60 and unique subunits of C70 were synthesized under mild conditions using metal-catalyzed protocols. According to X-ray crystallographic analyses, highly curved fragments of C60 have a maximum π-orbital axis vector (POAV) pyramidalization angle of up to 12.9 °, whereas distinctive fragments of C70, analogous to the tube portion of the rugby-shaped buckyball, are less curved. Among the eight buckybowls studied herein, five form polar crystals. Depending on the molecular geometry, the inversion dynamics of buckybowls involves either a planar or an S-shaped (non-planar) transition structure.

Nickel-catalyzed tetramerization of alkynes: synthesis and structure of octatetraenes.

In the presence of a catalytic system comprised of NiBr(2)(dppe) and Zn, arylacetylenes undergo tetramerization to form linear octatetraenes, generally in good to excellent yields. The structure of the coupling products was verified by X-ray crystallography.

Nickel-catalyzed, cascade cycloadditions of 1-ethynyl-8-halonaphthalenes with nitriles: synthesis, structure, and physical properties of new pyrroloarenes.

The reaction of 1-ethynyl-8-halonaphthalenes 1 with nitriles in the presence of the catalytic system [NiBr(2)(dppe)]/Zn (dppe=1,2-bis(diphenylphosphino)ethane) is found to produce unusual pyrroloarenes 2. The carbon-nitrogen triple bond in nitrile is activated twice, and five new bonds are formed in a one-pot transformation, which causes a pyrrole and two six-membered rings to be generated simultaneously. The scope and limitations of this reaction are examined. Similarly, alkyl-bridged diynes also furnish the corresponding polycycles. Diaryl-substituted cycloadducts 2 (R(1)=Ar) are fluxional, because of the restriction in rotation of the aryl groups. The rotational barrier is studied by performing (1)H NMR experiments at various temperatures. The structures of several compounds are determined by X-ray crystallographic analysis. The photophysical and electrochemical properties of the pyrroloarenes are also investigated.

Dinaphthozethrene and Diindenozethrene: Synthesis, Structural Analysis, and Properties

Zethrene-based condensed arenes dinaphthozethrene and diindenozethrene were synthesized by oxidative cyclodehydrogenation and palladium-catalyzed cyclization of 7,14-diarylzethrenes, respectively. Their structures were analyzed by X-ray crystallography. The photophysical and electrochemical properties of these compounds were investigated.