Investigations into ambient temperature biaryl coupling reactions

An Efficient Route to Biaryl Bisbenzocyclobutene Monomers Based on Suzuki Coupling Reaction at Room Temperature

An efficient and practical preparation of the bisbenzocyclobutene monomers has been developed via the room temperature Suzuki couplings of phenyl-1, 4-diboronic ester with 4-bromobenzocyclobutene or benzocyclobutene-4-boronic acid with aryl dibromides.

A Route to 4,4′-Bis(Benzocyclobutene) Based on Homocoupling Catalysed by Manganese or Iron Salts

An efficient and practical preparation of 4,4‘-bis(benzocyclobutene) has been developed by the room temperature homocoupling of 4-bromobenzocyclobutene with magnesium and an iron or manganese catalyst.

Electronic Properties of Furyl Substituents at Phosphorus and Their Influence on 31P NMR Chemical Shifts

The electronic properties of 2-furyl and 3-furyl substituents attached to phosphanes and phosphonium salts were studied by means of IR spectroscopy and experimental and computational (31)P NMR spectroscopy. The heteroaromatic systems proved to be electron withdrawing with respect to phenyl substituents. However, phosphorus atoms with attached furyl substituents are strongly shielded in NMR. The reason for this phenomenon was studied by solid state (31)P MAS NMR experiments. The chemical shift tensor was extracted, and the orientation within the molecules was determined. The tensor component sigma(33), which is effected the most by furyl systems, is oriented perpendicular to the P-C bonds of the substituents. P-furyl bonds are shorter than P-phenyl bonds. We assume therefore a lower ground-state energy of the molecules, because of the electron withdrawing properties of the 2-furyl systems. The sigma(para) component of the (31)P NMR magnetic shielding is therefore smaller, which results in an overall increase of the magnetic shielding.

A Microcapillary System for Simultaneous, Parallel Microwave-Assisted Synthesis

A continuous flow, microwave-assisted, parallel-capillary microreactor has been developed. Libraries of drug candidates were prepared on the milligram scale with this reactor by injecting plugs of reagents from separate syringes into common reaction capillaries, thereby producing discrete compounds in excellent yield and purity. Microwave irradiation provides the necessary energy that existing room-temperature microreactor technology lacks for higher activation barrier transformations, producing the required amounts of desired compounds in minutes or less.

Synthesis of 2-Nitro- and 2,2‘-Dinitrobiphenyls by Means of the Suzuki Cross-Coupling Reaction

[Reaction: see text]. Mechanistic investigations and protocols for the synthesis of 2-nitrobiphenyls and 2,2'-dinitrobiphenyls are disclosed. It is revealed that obstacles appear during the transmetalation step when the phenylboronic acid is substituted with a nitro group in the 2-position, whereas when substituted in the 3- or 4-positions, the reaction follows similar patterns as found in the electrophilic substitution of nitrobenzenes, an observation that may be attributed to the elimination step of the catalytic cycle.

A Microreactor for Microwave-Assisted Capillary (Continuous Flow) Organic Synthesis

A capillary-based flow system has been developed for conducting microscale organic synthesis with the aid of microwave irradiation. The capillary internal diameter investigated ranged from 200 to 1200 mum, while the flow rate was varied between 2 and 40 muL/min, which corresponds to the sample being irradiated approximately 4 min. Other parameters investigated include reaction concentration and power setting of the microwave. Excellent conversion was observed in a variety of cross coupling and ring-closing metathesis (RCM) reactions employing metal catalysts and in nucleophilic aromatic substitution and Wittig reactions that do not employ metals. Reactions that have solids in them do not seem to pose a significant concern for the method, such as blocked channels. It was shown that capillaries coated internally with thin films of Pd metal show tremendous rate accelerations and that the thin films themselves are capable of catalyzing Suzuki-Miyaura reactions with no exogenous catalyst added. Importantly, it has been demonstrated that reagents in separate syringes can be coinjected into the capillary, mix, and react with none of the laminar flow problems that plague microreactor (lab on a chip) technology. This paves the way to use microwave-assisted, flow capillary synthesis as a powerful and efficient means to replace "one-at-a-time" microwave synthesis to provide libraries of compounds in a scale suitable for biological screening purposes.

A Chiral Cyclohexanone Linked to Polystyrene for Solid-Phase Synthesis of Chiral α-Carbonyls

Two chiral cyclohexanones were linked to polystyrene resin. The polymer-bound auxiliaries were subjected to a sequence of four reactions, the last of which cleaves the desired alpha-chiral carbonyl compound off the resin, concurrently regenerating the resin-bound auxiliary in its original form. The resin can then be reused.

Direct synthesis of ferrocenylmethylphosphines from ferrocenylmethyl alcohols and their application as ligands for room temperature Pd(0)-catalyzed Suzuki cross-couplings of aryl bromides

[reaction: see text] The direct, high-yield conversion of readily available ferrocenylmethyl alcohols to ferrocenylmethylphosphines and the application of ferrocenylmethylphosphines as efficient ligands for room temperature Suzuki cross-coupling reaction of aryl bromides with phenylboronic acid are reported. The procedure of directly converting ferrocenylmethyl alcohols to ferrocenylmethylphosphines described here should find applications in the synthesis of many metallocenylmethylphosphines including optically active ones.