Koji Takagi

Organocatalytic Tail-to-Tail Dimerization of Olefin: Umpolung of Methyl Methacrylate Mediated by N-Heterocyclic Carbene

Highly selective tail-to-tail dimerization of methyl methacrylate has been realized by an N-heterocyclic carbene catalyst, giving dimethyl 2,5-dimethyl-2-hexenedioate with an E/Z ratio of 95:5 in 86% isolated yield. The umpolung mechanism is proposed on the basis of interception of the intermediates using ESI-MS analyses and deuterium-labeling experiments.

Experimental Mechanistic Studies of the Tail-to-Tail Dimerization of Methyl Methacrylate Catalyzed by N-Heterocyclic Carbene

We and others have previously reported the intermolecular umpolung reactions of Michael acceptors catalyzed by an N-heterocyclic carbene (NHC). The representative tail-to-tail dimerization of methyl methacrylate (MMA) has now been intensively investigated, leading to the following conclusions: (1) The catalysis involves the deoxy-Breslow intermediate, which is quite stable and remains active after the catalysis. (2) Addition of the intermediate to MMA and the final catalyst elimination are the rate-limiting steps. Addition of the NHC to MMA and the proton transfers are relatively very rapid. (3) The two alkenyl protons of the first MMA undergo an intermolecular transfer to C3 and C5 of the dimer. (4) The initial proton transfer is intermolecular. (5) Compared with the benzoin condensation, noticeable differences in the kinetics, reversibility, and stability of the intermediates are observed.

Triazine dendrimers by divergent and convergent methods

Two types of dendrimers with a 1,3,5-triazine ring at the branch point were synthesized by divergent and convergent methods. The divergent method began with 2,4,6-tris(p-nitroanilino)-1,3,5-triazine as a trifunctional core. Each cycle involved the reduction of the peripheral NO2 group followed by a reaction with 2-chloro-4,6-bis(p-nitroanilino)-1,3,5-triazine. The synthetic cycle was completed by the coupling with 2,4-dianilino-6-chloro-1,3,5-triazine (DACT) to eventually accomplish second-generation dendrimers ([G2]3-C) bearing 12 benzene rings at their edge. The convergent approach started with the reaction of DACT with p-nitrophenol to give rise to 2,4-dianilino-6-(p-nitrophenoxy)-1,3,5-triazine. The synthetic cycle consisted of reduction of the NO2 group and coupling with 2,4-dichloro-6-(p-nitrophenoxy)-1,3,5-triazine. The final step was the connection of each monodendron with cyanuric chloride to produce tridendron; in this way, the second-generation dendrimer ([EG2]3-C) was obtained. Gel permeation chromatography analyses indicated the aggregation of dendrimers in solution. Ultraviolet spectroscopic analyses revealed that the larger dendrimer had a more conjugated electron system from the core to the periphery. The thermal properties were evaluated by thermogravimetric analysis (TGA); excellent heat resistance was indicated, especially in [G1]3-C, which included alternately imine-like nitrogen-linked 1,3,5-triazine and benzene rings.

N-Heterocyclic carbene-catalyzed cyclotetramerization of acrylates.

N-Heterocyclic carbenes (NHCs) were found to catalyze the unprecedented cyclotetramerization of acrylates, producing the trisubstituted cyclopentenones in moderate yields. The proton or deuterium adducts of the deoxy-Breslow intermediate derived from NHC and two molecules of methyl acrylate were obtained. A reaction mechanism involving the new umpolung/cyclization sequence is proposed.

Design and synthesis of polymerizable cumulated double bond system. -Living coordination polymerization of alkylallenes by π-allylnickel catalyst-

Abstract The coordination polymerization of monoalkylallenes (2a; 1,2-nonadiene, 2b; 1,2-heptadiene, 2c; cyclohexylallene, 2d; t-butylallene) was carried out by [(π-allyl)NiOCOCF3]2 (1). The polymerization was found to proceed through a living process without any side reactions to yield soluble polymers in high yields, where the resulting polymers had predictable molecular weights and narrow molecular weight distributions. The coordination polymerization of dialkylallene (2e; 3-methyl-1,2-nonadiene, 2f; 2,3-nonadiene) was also carried out to obtain soluble polymers, although the polymerization rate of 2f was found to be considerably low compared with those of monoalkylallenes.

Block copolymerization of allene derivatives with isocyanides by the coordination polymerization with π‐allylnickel catalyst

A living block copolymerization of allene derivatives with 1-phenylethyl isocyanide (3) using [(allyl)NiOCOCF 3 ] 2 (1) is described. After complete polymerization of allene monomers such as n-octyloxyallene (2A) with 1, further addition of 3 to the reaction system yielded the corresponding block copolymers in high yield. For instance, a block copolymer (4A, M n = 39,600, M w /M n = 1.20) was obtained in 96% yield by the addition of 3 ([3]/[1] = 250) to the living solution of poly(n-octyloxyallene) (M n = 14,400, M w /M n = 1.03) prepared by the polymerization of 2A in the ratio of [2A]/[1] = 90. The resulting copolymer was a brownish orange gum or a solid, depending on the length of each of the segments. The solubility of the block copolymers could be controlled by the allene components. The copolymer of 2A with 3 having appropriate length of segments was soluble in n-hexane, while that of methoxyethoxyethoxyallene (2D) with 3 was soluble in methanol.

Self-Assembly of Oligothiophene Chromophores by m-Calix[3]amide Scaffold

m-Calix[3]amides carrying the bithiophene chromophore (BTC3A) and terthiophene chromophore (TTC3A) were synthesized by the cyclic trimerization of m-aminobenzoic acid esters for the purpose of the control and understanding of the self-assembly of oligothiophene chromophores. Polymers and model compounds were also prepared for comparison. From the (1)H NMR experiments, cyclic trimer BTC3A showed the syn/anti equilibrium in solution, and the syn/anti conformer ratio (76/24 in CDCl(3)) was influenced by the solvent character. Namely, the population of the syn conformer was lowest (70%) in THF-d(8) and was highest (86%) in CDCl(3)/CD(3)OD (1/1 in volume). On the other hand, the population of the syn conformer of cyclic trimer TTC3A was high (84%) even in CDCl(3). In a CHCl(3) solution of cyclic trimer BTC3A, the absorption maximum (342 nm) blue-shifted and the emission maximum (448 nm) red-shifted compared with those of polymer BTPA and model compound BTM. The solvent character also had an impact on the optical properties of cyclic trimer BTC3A. The red-shifted emission maximum (481 nm) of cyclic trimer BTC3A in CH(3)OH indicated the interaction between three bithiophene chromophores. The emission maxima of cyclic trimer TTC3A (486 nm) demonstrated a small red-shift from model compound TTM (477 nm), and no solvent dependency was observed, unlike cyclic trimer BTC3A.

RADICAL POLYMERIZATION OF METHYL METHACRYLATE WITH DIPHENYL DISELENIDE UNDER THERMAL OR PHOTOIRRADIATIONAL CONDITIONS

Polymerization of methyl methacrylate (MMA) with diphenyl diselenide (DPDSE) in the presence of AIBN at 60°C was investigated. DPDSE was worked as a chain transfer agent (CTA). The chain transfer constant (Ctr) of DPDSE for MMA was estimated to be 1.43. On the other hand, DPDSE was functioned as a photoiniferter for the photopolymerization of MMA. In a limited range of conversion, both the polymer yield and number average of molecular weight ([Mbar]n) increased with the reaction time, and the [Mbar]n linearly increased with the yield. The terminal structure of poly(MMA) was investigated by the 77Se NMR spectrum based on Methyl α-phenylseleno isobutylate (MSEPI) as model compound of the ω-chain end of poly(MMA). Further, photopolymerization of poly (MMA) containing phenylseleno group at ω-chain end as a polymeric photoiniferter with MMA effectively afforded a poly (MMA) having higher molecular weight.

Helicity Induction in Three π‐Conjugated Chromophores by Planar Chirality of Calixamide

Shall we twist? Three-dimensional arrangement of π-conjugated chromophores with triple-stranded helicity was achieved by using the planar chirality of m-calix[3]amide. Based on spectroscopic data and theoretical calculations, the dynamic and preferred helical characters of bithiophene units embedded in the tubular molecule were elucidated, and the absolute configuration was determined.

Synthesis of star polystyrene by radical polymerization with 1,2,4,5-tetrakis(p-tert-butylphenyl selenomethyl)benzene as a novel photoiniferter

Abstract 1,2,4,5-Tetrakis(p-tert-butylphenylselenomethyl)benzene was synthesized and used as a tetrafunctional photoiniferter for the polymerization of styrene. Both the yield and the number average molecular weight ( M n ) of polymers increased with reaction time and M n linearly increased with yield of polymer. The polymerization of styrene using this novel photoiniferter permitted formation of star-shaped polystyrene containing arylseleno groups at the chain ends, and the average degree of functionality was 3.2. Photopolymerization of styrene with end-functional star polystyrene as polymeric photoiniferter afforded polystyrene having high molecular weight.