Catalytic Enantioselective Desymmetrization of <i>meso</i>-Glutaric Anhydrides Using a Stable Ni₂-Schiff Base Catalyst

We describe the desymmetrization of <i>meso</i>-glutaric anhydrides to chiral hemiesters using a bench-stable homodinuclear Ni₂-(Schiff base) complex as the catalyst in good to excellent yield (up to 99%) and enantioselectivity (up to 94%). Using the opposite enantiomer of the catalyst, we obtained the same yield and enantioselectivity with the opposite configuration, thereby gaining access to both hemiester enantiomers

Studies on Catalytic Enantioselective Total Synthesis of Caprazamycin B: Construction of the Western Zone

We describe a simple and convenient synthesis of the western zone of caprazamycin B using two catalytic asymmetric reactions as key elements of our approach. Desymmetrization of 3-methylglutaric anhydride with the (<i>S</i>)-Ni₂-(Schiff base) complex as a catalyst furnished the chiral hemiester, and a thioamide-aldol reaction with mesitylcopper, (<i>R</i>,<i>R</i>)-Ph-BPE, and 2,2,5,7,8-pentamethylchromanol as a catalyst furnished the β-hydroxy thioamide in good yield and enantioselectivity. On further transformation, the thioamide functionality was converted to the corresponding β-hydroxy ester. Finally, a convergent synthesis of the western zone of caprazamycin B was achieved by connecting the hemiester, the β-hydroxy ester, and the 2,3,4-tri-<i>O</i>-methyl-l-rhamnose fragments

Precise Synthesis of Dendrimer-like Star-Branched Poly(<i>tert</i>-butyl methacrylate)s and Their Block Copolymers by a Methodology Combining α-Terminal-Functionalized Living Anionic Polymers with a Specially Designed Linking Reaction in an Iterative Fashion

A new stepwise iterative methodology was developed for the synthesis of well-defined high-generation and high-molecular-weight dendrimer-like star-branched poly­(<i>tert</i>-butyl methacrylate)­s (P^tBMA)­s and block copolymers composed of P^tBMA and polystyrene (PS) segments. The methodology involves the following two reaction steps in an iterative process: (1) a linking reaction based on a 1:1 addition reaction of an α-terminal-(3-<i>tert</i>-butyldimethylsilyloxymethylphenyl (SMP))₂-functionalized living polymer with a core compound or α-terminal-(α-phenyl acrylate (PA))₂-functionalized polymers linked to the core and (2) a conversion of the SMP group to the PA function, to be used as the next reaction site. Repetition of the two reaction steps, (1) and (2), allows for the synthesis of high-generation and high-molecular-weight dendrimer-like star-branched polymers. In practice, a series of dendrimer-like star-branched (P^tBMA)­s up to the fifth generation (5G) were successfully synthesized. The resulting polymers, whose arm segments were four-branched at the core and two-branched at each layer, were all well-defined in branched architecture and precisely controlled in chain length, and the final 5G dendrimer-like star-branched P^tBMA possessed a predictable <i>M</i>_n value of 1.07 × 10⁷ g/mol and an extremely narrow molecular weight distribution of 1.03 in <i>M</i>_w/<i>M</i>_n value. The synthetic possibility of similar dendrimer-like star-branched polymers composed of functional polymer segments bearing acid-labile and/or basic groups by the same methodology was also demonstrated. Furthermore, 4G dendritic architectural block copolymers with hierarchic layer structures composed of P^tBMA (and poly­(methacrylic acid)) and PS segments were synthesized

Seeded Emulsion Polymerization of Styrene in the Presence of Water-Swollen Hydrogel Microspheres

In a previous study, we have ascertained that the charge distribution in hydrogel microspheres (microgels) plays a crucial role in controlling the nanocomposite structure of the polystyrene obtained from the seeded emulsion polymerization (SEP) of styrene in the presence of microgels. However, all these polymerizations were conducted at high temperature, where most of these microgels were dehydrated and deswollen. In the present study, we initially verified that the nanocomposite microgels can be synthesized even when the seed microgels are swollen and hydrated during the SEP of styrene. These highly swollen microgels were used as the nucleation sites for the polystyrene, and subsequently the propagation of the hydrophobic polystyrenes proceeded within water-swollen microgels

Localization of Polystyrene Particles on the Surface of Poly(<i>N</i>‑isopropylacrylamide-<i>co</i>-methacrylic acid) Microgels Prepared by Seeded Emulsion Polymerization of Styrene

Composite microgels with polystyrene nanoparticles were synthesized by seeded emulsion polymerization of styrene in the presence of pH- and temperature-responsive poly­(<i>N</i>-isopropylacrylamide-<i>co</i>-methacrylic acid) microgels as seeds. In particular, the core microgels maintained their swelled state as the pH was increased to 10 during seeded emulsion polymerization conducted at an elevated temperature. Furthermore, we tuned the swelling degree of the core microgels at pH 10 by changing the amount of methacrylic acid incorporated during the synthesis of the core microgels. Unlike deswollen microgels, during the seeded emulsion polymerization, the swollen microgels were covered with a monolayer of non-close-packed polystyrene particles on their surface, as confirmed by electron microscopy. A possible mechanism for the seeded emulsion polymerization of styrene in the presence of swollen microgels under alkaline conditions is proposed

Seeded Emulsion Polymerization of Styrene in the Presence of Water-Swollen Hydrogel Microspheres

In a previous study, we have ascertained that the charge distribution in hydrogel microspheres (microgels) plays a crucial role in controlling the nanocomposite structure of the polystyrene obtained from the seeded emulsion polymerization (SEP) of styrene in the presence of microgels. However, all these polymerizations were conducted at high temperature, where most of these microgels were dehydrated and deswollen. In the present study, we initially verified that the nanocomposite microgels can be synthesized even when the seed microgels are swollen and hydrated during the SEP of styrene. These highly swollen microgels were used as the nucleation sites for the polystyrene, and subsequently the propagation of the hydrophobic polystyrenes proceeded within water-swollen microgels

Seeded Emulsion Polymerization of Styrene in the Presence of Water-Swollen Hydrogel Microspheres

In a previous study, we have ascertained that the charge distribution in hydrogel microspheres (microgels) plays a crucial role in controlling the nanocomposite structure of the polystyrene obtained from the seeded emulsion polymerization (SEP) of styrene in the presence of microgels. However, all these polymerizations were conducted at high temperature, where most of these microgels were dehydrated and deswollen. In the present study, we initially verified that the nanocomposite microgels can be synthesized even when the seed microgels are swollen and hydrated during the SEP of styrene. These highly swollen microgels were used as the nucleation sites for the polystyrene, and subsequently the propagation of the hydrophobic polystyrenes proceeded within water-swollen microgels

Seeded Emulsion Polymerization of Styrene in the Presence of Water-Swollen Hydrogel Microspheres

In a previous study, we have ascertained that the charge distribution in hydrogel microspheres (microgels) plays a crucial role in controlling the nanocomposite structure of the polystyrene obtained from the seeded emulsion polymerization (SEP) of styrene in the presence of microgels. However, all these polymerizations were conducted at high temperature, where most of these microgels were dehydrated and deswollen. In the present study, we initially verified that the nanocomposite microgels can be synthesized even when the seed microgels are swollen and hydrated during the SEP of styrene. These highly swollen microgels were used as the nucleation sites for the polystyrene, and subsequently the propagation of the hydrophobic polystyrenes proceeded within water-swollen microgels

Seeded Emulsion Polymerization of Styrene in the Presence of Water-Swollen Hydrogel Microspheres

In a previous study, we have ascertained that the charge distribution in hydrogel microspheres (microgels) plays a crucial role in controlling the nanocomposite structure of the polystyrene obtained from the seeded emulsion polymerization (SEP) of styrene in the presence of microgels. However, all these polymerizations were conducted at high temperature, where most of these microgels were dehydrated and deswollen. In the present study, we initially verified that the nanocomposite microgels can be synthesized even when the seed microgels are swollen and hydrated during the SEP of styrene. These highly swollen microgels were used as the nucleation sites for the polystyrene, and subsequently the propagation of the hydrophobic polystyrenes proceeded within water-swollen microgels

Seeded Emulsion Polymerization of Styrene in the Presence of Water-Swollen Hydrogel Microspheres

In a previous study, we have ascertained that the charge distribution in hydrogel microspheres (microgels) plays a crucial role in controlling the nanocomposite structure of the polystyrene obtained from the seeded emulsion polymerization (SEP) of styrene in the presence of microgels. However, all these polymerizations were conducted at high temperature, where most of these microgels were dehydrated and deswollen. In the present study, we initially verified that the nanocomposite microgels can be synthesized even when the seed microgels are swollen and hydrated during the SEP of styrene. These highly swollen microgels were used as the nucleation sites for the polystyrene, and subsequently the propagation of the hydrophobic polystyrenes proceeded within water-swollen microgels