One-step catalytic asymmetric synthesis of all-syn deoxypropionate motif from propylene: Total synthesis of (2R,4R,6R,8R)-2,4,6,8-tetramethyldecanoic acid

Polystyrene Chain Growth Initiated from Dialkylzinc for Synthesis of Polyolefin-Polystyrene Block Copolymers

Polyolefins (POs) are the most abundant polymers. However, synthesis of PO-based block copolymers has only rarely been achieved. We aimed to synthesize various PO-based block copolymers by coordinative chain transfer polymerization (CCTP) followed by anionic polymerization in one-pot via conversion of the CCTP product (polyolefinyl)2Zn to polyolefinyl-Li. The addition of 2 equiv t-BuLi to (1-octyl)2Zn (a model compound of (polyolefinyl)2Zn) and selective removal or decomposition of (tBu)2Zn by evacuation or heating at 130 °C afforded 1-octyl-Li. Attempts to convert (polyolefinyl)2Zn to polyolefinyl-Li were unsuccessful. However, polystyrene (PS) chains were efficiently grown from (polyolefinyl)2Zn; the addition of styrene monomers after treatment with t-BuLi and pentamethyldiethylenetriamine (PMDTA) in the presence of residual olefin monomers afforded PO-block-PSs. Organolithium species that might be generated in the pot of t-BuLi, PMDTA, and olefin monomers, i.e., [Me2NCH2CH2N(Me)CH2CH2N(Me)CH2Li, Me2NCH2CH2N(Me)Li·(PMDTA), pentylallyl-Li⋅(PMDTA)], as well as PhLi⋅(PMDTA), were screened as initiators to grow PS chains from (1-hexyl)2Zn, as well as from (polyolefinyl)2Zn. Pentylallyl-Li⋅(PMDTA) was the best initiator. The Mn values increased substantially after the styrene polymerization with some generation of homo-PSs (27-29%). The Mn values of the extracted homo-PS suggested that PS chains were grown mainly from polyolefinyl groups in [(polyolefinyl)2(pentylallyl)Zn]-[Li⋅(PMDTA)]+ formed by pentylallyl-Li⋅(PMDTA) acting onto (polyolefinyl)2Zn.

Copper-Catalyzed Asymmetric Conjugate Additions of Bis(pinacolato)diboron and Dimethylzinc to Acyl- N-methylimidazole Michael Acceptors: A Highly Stereoselective Unified Strategy for 1,3,5,... n (OH, Me) Motif Synthesis

A unified strategy for the construction of prevalent 1,3,5,... n (OH, Me) motifs based on consecutive copper-catalyzed asymmetric conjugate borylation (ACB) and methylation (ACA) reactions involving α,β-unsaturated 2-acyl- N-methylimidazoles is described. Good yields and high diastereoselectivities have been obtained in ACA and ACB reactions for both matched and mismatched pairs as illustrated in the synthesis of syn/ anti and anti/ anti (Me, OTBS, Me) and (OH, OTBS, Me) motifs.

Single-Step Construction of the anti-Deoxypropionate Motif from Propylene: Formal Total Synthesis of the Cuticular Hydrocarbons Isolated from Antitrogus parvulus

Reported herein is the single-step construction of an anti-configured deoxypropionate motif by syndiospecific propylene oligomerization catalyzed by a C_s -symmetric zirconocene complex. After oligomerization, oxidation of the oligomers by oxygen afforded oligopropylene alcohols in a single step. This strategy was applied to the single-step preparation of rel-(2R,4S,6R,8S)-2,4,6,8-tetramethylundecan-1-ol, the racemic mixture of the synthetic fragment of the cuticular hydrocarbons isolated from the cane beetle Antitrogus parvulus.

Iterative Synthesis of Polydeoxypropionates Based on Iridium-Catalyzed Asymmetric Hydrogenation of α-Substituted Acrylic Acids

A novel iterative protocol for the synthesis of polydeoxypropionates was developed based on iridium-catalyzed asymmetric hydrogenation of α-substituted acrylic acids. The catalyst loading can be as low as 0.01 mol %, and the overall yield for one iterative cycle is >76%. The reaction conditions are mild, and no organometallic reagents or chromatography steps are required. Using this protocol, (+)-phthioceranic acid and the polydeoxypropionate motifs of ionomycin and borrelidin were synthesized in high yield.

Polystyrene Chain Growth from Di-End-Functional Polyolefins for Polystyrene-Polyolefin-Polystyrene Block Copolymers

Triblock copolymers of polystyrene (PS) and a polyolefin (PO), e.g., PS-block-poly(ethylene-co-1-butene)-block-PS (SEBS), are attractive materials for use as thermoplastic elastomers and are produced commercially by a two-step process that involves the costly hydrogenation of PS-block-polybutadiene-block-PS. We herein report a one-pot strategy for attaching PS chains to both ends of PO chains to construct PS-block-PO-block-PS directly from olefin and styrene monomers. Dialkylzinc compound containing styrene moieties ((CH₂=CHC₆H₄CH₂CH₂)₂Zn) was prepared, from which poly(ethylene-co-propylene) chains were grown via "coordinative chain transfer polymerization" using the pyridylaminohafnium catalyst to afford di-end functional PO chains functionalized with styrene and Zn moieties. Subsequently, PS chains were attached at both ends of the PO chains by introduction of styrene monomers in addition to the anionic initiator Me₃SiCH₂Li·(pmdeta) (pmdeta = pentamethyldiethylenetriamine). We found that the fraction of the extracted PS homopolymer was low (~20%) and that molecular weights were evidently increased after the styrene polymerization (ΔM_n = 27⁻54 kDa). Transmission electron microscopy showed spherical and wormlike PS domains measuring several tens of nm segregated within the PO matrix. Optimal tensile properties were observed for the sample containing a propylene mole fraction of 0.25 and a styrene content of 33%. Finally, in the cyclic tensile test, the prepared copolymers exhibited thermoplastic elastomeric properties with no breakage up over 10 cycles, which is comparable to the behavior of commercial-grade SEBS.

Preparation of polystyrene–polyolefin multiblock copolymers by sequential coordination and anionic polymerization

The polyolefin and polystyrene chains were successively grown from [4-(isopropenyl)benzyl]₂Zn to form polystyrene-b-polyolefin-b-polystyrene units.