Motohiro Sonoda

Catalytic C-H/olefin coupling

The cleavage and addition of ortho C-H bonds in various aromatic compounds such as ketones, esters, imines, imidates, nitrile, and aldehydes to olefins and acetlylenes can be achieved catalytically with the aid of ruthenium catalysts. The reaction is generally highly efficient and useful in synthetic methods. The coordination to the metal center by a heteroatom in directing groups such as carbonyl and imino groups is the key. The reductive elimination to form a C-C bond is the rate-determining step.

Directing effect of functional groups in ruthenium-catalyzed addition of substituted acetophonones to an olefin

Abstract Ruthenium-catalyzed addition of 3′-methyl-, 3′-trifluoromethyl-, and 3′- N , N -dimethylaminoacetophenones to an olefin proceeds site selectively at 6′ Cue5f8H bonds to give the 1:1 Cue5f8H/olefin addition products in high yields. In contrast, the addition of 3′-methoxyacetophenone takes place preferentially at the Cue5f8H bond at the more congested 2′ position.

Polyyne cyclization to form carbon cages: [16.16.16](1,3,5)cyclophanetetracosayne derivatives C60H6 and C60Cl6 as precursors to C60 fullerene

Abstract [16.16.16](1,3,5)Cyclophanes fused by six [4.3.2]propellatriene units, which would serve as precursors to cage polyyne C 60 H 6 and its perchloro derivative C 60 Cl 6 , respectively, were prepared. In the negative mode laser desorption mass spectra of the cyclophanes, the polyyne anions C 60 H 6 − and C 60 Cl 6 − were detected. Moreover, size-selective formation of C 60 + as well as C 60 − was also observed, indicating the possible polyyne cyclization mechanism to form the fullerene cage.

Synthesis of butadiyne-bridged [4n] metacyclophanes having exo-annular t-butyl groups

Abstract Butadiyne-bridged [4 4 ]- and [4 8 ]metacyclophanes having exo -annular t -butyl groups were prepared by intermolecular Eglinton coupling of the dimeric unit or by intramolecular ring closure of the linear tetramer. Comparison of the 1 H and 13 C NMR spectra of [4 4 ]metacyclophane with those of [4 8 ]cyclophane and diphenylbutadiyne revealed its prominent geometrical feature due to deformation of the triple bonds from linearity. The [4 4 ]Metacyclophane was converted into [0 8 ]thiophenometacyclophane in good yield by treatment with sodium sulfide.

Vinylidene to alkyne rearrangement to form polyynes: synthesis and photolysis of dialkynylmethylenebicyclo[4.3.1]deca-1,3,5-triene derivatives

Abstract Dialkynylmethylenebicyclo[4.3.1]deca-1,3,5-triene derivatives were synthesized as precursors to generate dialkynylvinylidenes by extrusion of an aromatic fragment, indane. Photolysis of the trienes gave linear polyynes as the major products produced by rearrangement of the vinylidenes, together with the isomerization products having a methylenecycloheptatriene moiety.

Molecular Propellers that Consist of Dehydrobenzo[14]annulene Blades

A new class of propel- ler-shaped compound (4), which consisted of dehydrobenzo[14]annulene ([14]DBA) blades, as well as its naphtho homologues (5 and 6), have been prepared. Although NMR studies of compound 4 did not provide useful information regarding its conformation in solution, DFT calculations with different functionals and the 6-31G* basis set all indicated that the D(3)-symmetric structure was energetically more favorable than the C(2) conformer. From X-ray crystallographic analysis, it appeared that compound 4 adopted a propeller-shaped-, approximately D(3)-symmetric structure in the solid state, in which the [14]DBA blades were twisted substantially owing to steric repulsion between the neighboring benzene rings. On the contrary, in the case of compound 6, although the DFT calculations with the B3LYP functional predicted that the D(3)-symmetric conformation was more stable, calculations with the M05 and M05-2X functionals indicated that the C(2) conformer was more favorable because of π-π interactions between the naphthalene units of a pair of neighboring blades. Indeed, X-ray analysis of compound 6 showed that it adopted an approximately C(2)-symmetric conformation. Moreover, on the basis of variable-temperature (1)H NMR measurements, we found that compound 6 adopted a C(2) conformation and the barrier for interconversion between the C(2)-C(2) conformers was estimated to be 16.2 kcal mol(-1); however, no indication of the presence of the D(3) isomer was obtained. The relatively small energy barriers to interconversion, despite the large overlapping of neighboring blades, was ascribed to the flexibility of the acetylene linkages, which could be deformed substantially in the transition state of the ring-flip.

Flash vacuum pyrolysis of 1,6-diphenyl-1,5-hexadien-3-ynes: tandem diaryldienyne cyclizations to form chrysene

Flash vacuum pyrolysis of 1,6-diphenyl-1,5-hexadien-3-yne at 1000°C and its bromo derivative at 800°C yielded chrysene as the major product through tandem diaryldienyne cyclizations.

PtCl2-Catalyzed Cyclization of o-Diethynylbenzene Derivatives Triggered by Intramolecular Nucleophilic Attack

Abstract PtCl2-catalyzed cyclization of o-diethynylbenzene derivatives bearing a hydroxyethyl group yielded naphthofuran derivatives by initial intramolecular cyclization of the hydroxy group to an activated ethynyl group followed by attack of the second ethynyl group to a vinylplatinum intermediate. When the ethynyl terminal is substituted by a hydroxypropyl group, not only homologous naphthodihydropyran but also indenylidenetetrahydrofuran derivatives were formed.

Selective Metallation of 3-Halothiophenes: Practical Methods for the Synthesis of 2-Bromo-3-formylthiophene

Abstract Selective lithiation of 3-bromothiophene was accomplished under controlled conditions without formation of undesired thienyllithium compounds. A thienyl Grignard reagent derived from 2-bromo-3-iodothiophene was transformed into 2-bromo-3-formylthiophene in high selectivity by formylation with dimethylformamide (DMF) at optimal reaction temperature.