RAFT Polymerisation by the Radical Decarboxylation of Carboxylic Acids.

The controlled grafting of polymers from small- and macro-molecular substrates is an essential process for many advanced polymer applications. This usually requires the pre-functionalisation of substrates with an appropriate functional group, such as a RAFT agent or ATRP initiator, which requires additional synthetic steps. In this paper, we describe the direct grafting of RAFT polymers from carboxylate containing small molecules and polymers via photochemical radical decarboxylation.

Carbon fibre surface modification facilitated by silver-catalysed radical decarboxylation.

A silver catalysed radical decarboxylation process was used to graft a copolymer (4 : 1; methylacrylate/acrylic acid) onto short carbon fibres. Surface grafting was confirmed by XPS, SEM and TGA, suggesting that the polymer accounted for 10% of the modified materials mass. Incorporation of these surface enhanced carbon fibres into an epoxy resin gave composites demonstrating an increase in ductility and a clear change in failure mode from adhesive, at the fibre-matrix interface, to cohesive, within the matrix polymer itself.

Enantioselective Synthesis of Pyrrolidines by a Phosphine-Catalyzed γ-Umpolung/β-Umpolung Cascade.

Herein, we report an enantioselective catalytic annulation of electron-poor allenes with aminocrotonates. The reaction proceeds by the umpolung γ-amination of the allenoate and β-umpolung intramolecular conjugate addition. The reaction provides ready access to pyrrolidines using a homochiral phosphepine catalyst, which allows most products to form in good yields (55-85%) with ≥95:5 er and ≥4:1 dr.

Polymer End Group Control through a Decarboxylative Cobalt-Mediated Radical Polymerization: New Avenues for Synthesizing Peptide, Protein, and Nanomaterial Conjugates.

Cobalt-mediated radical polymerizations (CMRPs) have been initiated by the radical decarboxylation of tetrachlorophthalimide activated esters. This allows for the controlled radical polymerization of activated monomers across a broad temperature range with a single cobalt species, with the incorporation of polymer end groups derived from simple carboxylic acid derivatives and termination with an organozinc reagent. This method has been applied to the synthesis of a polymer/graphene conjugate and a water-soluble protein/polymer conjugate, demonstrating the first examples of CMRP in graphene and protein conjugation.

Thermoresponsive Poly(-isopropylacrylamide) Grafted from Cellulose Nanofibers Silver-Promoted Decarboxylative Radical Polymerization.

A family of thermoresponsive poly(-isopropylacrylamide) [PNIPAM]-grafted cellulose nanofibers (CNFs) was synthesized a novel silver-promoted decarboxylative polymerization approach. This method relies on the oxidative decarboxylation of carboxylic acid groups to initiate free radicals on the surface of CNFs. The polymerization reaction employs relatively mild reaction conditions and can be performed in a one-step, one-pot fashion.

Redox Isomerization/(3+2) Allenoate Annulation by Auto-Tandem Phosphine Catalysis.

A phosphine-catalyzed approach to pyrrolines has been developed that involves two mechanistically unlinked catalytic processes. The first involves the redox isomerization of amino crotonates to provide access to aliphatic tosyl imines, which then engage in a (3+2) annulation with various allenoates. The reaction shows generality, with 24 examples established, along with a low yielding and moderately enantioselective variant.

Pristine Graphene as a Racemization Catalyst for Axially Chiral BINOL.

Despite versatile applications of functionalized graphene in catalysis, applications of pure, unfunctionalized graphene in catalysis are in their infancy. This work uses both computational and experimental approaches to show that single-layer graphene can efficiently catalyze the racemization of axially chiral BINOL in solution. Using double-hybrid density functional theory (DHDFT) we calculate the uncatalyzed and catalyzed Gibbs free reaction barrier heights in a number of representative solvents of varying polarity: benzene, diphenyl ether, dimethylformamide (DMF), and water.

RAFT polymer cross-coupling with boronic acids.

The ability to modify the thiocarbonylthio end-groups of RAFT polymers is important for applications where an inert or highly functionalised material is required. Here we report a copper promoted cross-coupling reaction between RAFT polymer end-groups and aryl boronic acids. This method gives high conversion to the modified polymers, and is compatible with a wide variety of functional molecules.

Oxidative Cross-Coupling of Boron and Antimony Nucleophiles via Palladium(I).

The use of an isolatable, monomeric Pd(I) complex as a catalyst for the oxidative cross-coupling of aryl-antimony and aryl-boron nucleophiles is reported. This reaction tolerates a wide variety of substrates, with >20:1 selectivity for cross-coupled products. This strategy offers a new approach to achieving the selective cross-coupling of nucleophiles.

Phosphine catalysed (5 + 1) annulation of ynone/cinnamates with primary amines.

The (5 + 1) annulation of ynone/cinnamates and related substrates with protected primary amines gives rise to isoquinolones, pyrrolidinones and pyrrolopiperazines in good to excellent yields under phosphine catalysis. The reaction is viable with chiral phosphines, although the selectivity is poor.

α-Amino Aldehydes as Readily Available Chiral Aldehydes for Rh-Catalyzed Alkyne Hydroacylation.

Readily available α-amino aldehydes, incorporating a methylthiomethyl (MTM) protecting group on nitrogen, are shown to be efficient substrates in Rh-catalyzed alkyne hydroacylation reactions. The reactions are performed under mild conditions, employing a small-bite-angle bis-phosphine ligand, allowing for good functional group tolerance with high stereospecificity. Amino aldehydes derived from glycine, alanine, valine, leucine, phenylalanine, isoleucine, serine, tryptophan, methionine, and cysteine were successfully employed, as was an enantiomerically enriched α-OMTM-aldehyde derived from phenyllactic acid.

Medium-Ring Effects on the Endo/Exo Selectivity of the Organocatalytic Intramolecular Diels-Alder Reaction.

The intramolecular Diels-Alder reaction has been used as a powerful method to access the tricyclic core of the eunicellin natural products from a number of 9-membered-ring precursors. The endo/exo selectivity of this reaction can be controlled through a remarkable organocatalytic approach, employing MacMillan's imidazolidinone catalysts, although the mechanistic origin of this selectivity remains unclear. We present a combined experimental and density functional theory investigation, providing insight into the effects of medium-ring constraints on the organocatalyzed intramolecular Diels-Alder reaction to form the isobenzofuran core of the eunicellins.

A general method for interconversion of boronic acid protecting groups: trifluoroborates as common intermediates.

We have developed a general protocol for the interconversion of diverse protected boronic acids, via intermediate organotrifluoroborates. N-Methyliminodiacetyl boronates, which have been hitherto resistant to direct conversion to trifluoroborates, have been shown to undergo fluorolysis at elevated temperatures. Subsequent solvolysis of organotrifluoroborates in the presence of trimethylsilyl chloride and a wide range of bis-nucleophiles enables the generation of a variety of protected boronic acids.

Activating group recycling in action: a rhodium-catalyzed carbothiolation route to substituted isoquinolines.

A new rhodium(I) catalyst allows practical and efficient alkyne carbothiolation reactions to be achieved on synthetically useful ketone-bearing aryl methyl sulfides. The carbothiolation adducts, featuring a 'recycled methyl sulfide' activating group, are convenient precursors to highly substituted isoquinolines.

Traceless chelation-controlled rhodium-catalyzed intermolecular alkene and alkyne hydroacylation.

A new functional-group tolerant, rhodium-catalyzed, sulfide-reduction process is combined with rhodium-catalyzed chelation-controlled hydroacylation reactions to give a traceless hydroacylation protocol. Aryl- and alkenyl aldehydes can be combined with both alkenes, alkynes and allenes to give traceless products in high yields. A preliminary mechanistic proposal is also presented.

Intermolecular hydroacylation: high activity rhodium catalysts containing small-bite-angle diphosphine ligands.

Readily prepared and bench-stable rhodium complexes containing methylene bridged diphosphine ligands, viz. [Rh(C(6)H(5)F)(R(2)PCH(2)PR'(2))][BAr(F)(4)] (R, R' = (t)Bu or Cy; Ar(F) = C(6)H(3)-3,5-(CF(3))(2)), are shown to be practical and very efficient precatalysts for the intermolecular hydroacylation of a wide variety of unactivated alkenes and alkynes with β-S-substituted aldehydes. Intermediate acyl hydride complexes [Rh((t)Bu(2)PCH(2)P(t)Bu(2))H{κ(2)(S,C)-SMe(C(6)H(4)CO)}(L)](+) (L = acetone, MeCN, [NCCH(2)BF(3)](-)) and the decarbonylation product [Rh((t)Bu(2)PCH(2)P(t)Bu(2))(CO)(SMePh)](+) have been characterized in solution and by X-ray crystallography from stoichiometric reactions employing 2-(methylthio)benzaldehdye.

Aryl methyl sulfides as substrates for rhodium-catalyzed alkyne carbothiolation: arene functionalization with activating group recycling.

A Rh(I)-catalyzed method for the efficient functionalization of arenes is reported. Aryl methyl sulfides are combined with terminal alkynes to deliver products of carbothiolation. The overall process results in reincorporation of the original arene functional group, a methyl sulfide, into the products as an alkenyl sulfide.

O-substituted alkyl aldehydes for rhodium-catalyzed intermolecular alkyne hydroacylation: the utility of methylthiomethyl ethers.

Combining α-methylthiomethyl (MTM) ether substituted aldehydes and 1-alkynes in the presence of [Rh(dppe)]ClO(4) results in efficient intermolecular alkyne hydroacylation to deliver α-O-MTM-substituted enone products. The product MTM ethers can be converted to the free hydroxyl group either in situ, by the addition of water to the completed reaction, or in a separate operation, by the action of silver nitrate.