Paul Sampson

Ring fluorinated thiophenes: applications to liquid crystal synthesis

Abstract Ring fluorinated thiophenes were synthesized via a Balz–Schiemann fluorination approach and were successfully employed in the synthesis of liquid crystals using regioselective electrophilic bromination and regioselective Suzuki coupling chemistry.

Synthesis and mesomorphic properties of 1,1-difluoroalkyl-substituted biphenylthienyl and terphenyl liquid crystals. A comparative study of mesomorphic behavior relative to alkyl, alkoxy and alkanoyl analogs

A variety of biphenylthienyl and terphenyl-based liquid crystalline materials were prepared that incorporate a 1,1-difluoropentyl terminal group. The mesogenic properties of these compounds were compared and contrasted with analogs where the CF2 moiety was replaced by a -CH2-, -O- or -CO- group. The 1,1-difluoroalkyl group is unique in its behavior and tends to promote orthogonal smectic phase behavior.

Synthesis and stability of 2-(1,1-difluoroalkyl) thiophenes and related 1,1-difluoroalkyl benzenes: fluorinated building blocks for liquid crystal synthesis

Abstract The synthesis of a series of 2-(1,1-difluoroalkyl) thiophenes, including some biphenylthienyl liquid crystalline materials, was examined using a variety of fluorination approaches. For comparison purposes, a series of 1,1-difluoroalkyl benzene analogs were also prepared. The direct fluorodeoxygenation of alkyl thienyl ketones and alkyl phenyl ketones using various aminofluorosulfuranes proceeded in only moderate to poor yields. In contrast, fluorodesulfurization of the corresponding 1,3-dithiolanes using NOBF4/PPHF cleanly afforded the desired 2-(1,1-difluoroalkyl) thiophenes (and analogous 1,1-difluoroalkyl benzenes) in high yields. Fluorodesulfurization of 2-alkyl-2-thienyl-1,3-dithiolanes using NBS (or DBH)/PPHF was complicated by competing ring and/or side chain bromination pathways. These problems were avoided when using NIS/PPHF. Although the various 1,1-difluoroalkyl arene products were sensitive to hydrolytic decomposition on prolonged exposure to silica, the purified products proved quite stable and were well suited for use as building blocks for liquid crystal synthesis.

Novel 5-(4-alkoxyphenyl)thieno[3,2-b]thiophene-2-carboxylate esters: Highly efficient synthesis and mesogenic evaluation of a new class of materials exhibiting the smectic C phase

A series of alkyl 5-(4-alkoxyphenyl)thieno[3,2-b]thiophene-2-carboxylates were prepared via a direct, efficient Pd(0)-catalysed Suzuki–Miyaura coupling approach. A series of long-chain alkyl thieno[3,2-b]thiophene-2-carboxylate esters, synthesised from newly reported alkyl mercaptoacetates, were elaborated into the target compounds via regioselective (C-5) halogenation followed by cross-coupling with 4-alkoxyphenyltrifluoroborate salts. As expected, these target alkyl 5-(4-alkoxyphenyl)thieno[3,2-b]thiophene-2-carboxylate ester mesogens exhibited the orthogonal smectic A phase; notably, they are the first materials built on the thieno[3,2-b]thiophene motif to also exhibit the smectic C mesophase.

Synthesis of β-fluoro-α,β-unsaturated esters and nitriles via a fluoro-pummerer rearrangement

Abstract A 5-step synthesis of terminally unsaturated β-fluoro-α, β -unsaturated esters and nitriles 1 is described. Substantial amounts of a deoxygenative side reaction were observed during the key fluoro-Pummerer rearrangement step in the routes leading to the nitriles 1c and 1d .

1,3,4-Thiadiazole-2-carboxylate esters: new synthetic methodology for the preparation of an elusive family of self-organizing materials

A series of alkyl 5-(4-octyloxyphenyl)-1,3,4-thiadiazole-2-carboxylates has been prepared via a novel chemoselective ring-closure of appropriate tricarbonyl precursors. This paper represents the first report of a general and reproducible synthetic methodology for the preparation of 1,3,4-thiadiazole-2-carboxylate esters. The 1,3,4-thiadiazole esters synthesized were designed to evaluate the feasibility of this new core unit for potential ferroelectric applications. The core unit was found to promote strongly the formation of tilted smectic phases (the smectic C phase in particular). The 1,3,4-thiadiazole ester was found to be a stronger promoter of the smectic C phase than its phenyl-based counterpart.

The synthesis and mesogenic behaviour of the first series of low molar mass thieno[3,2-b]thiophene-2-carboxylate ester-based mesogens

The synthesis of a family of alkyl 5-(4-hexyloxyphenyl)thieno[3,2-b]thiophene-2-carboxylate liquid crystals is described. The synthetic methodology utilised includes a Fiesselmann synthesis of the thieno[3,2-b]thiophene core, and the first report of a completely regioselective α-bromination of the resulting thieno[3,2-b]thiophene-2-carboxylate ester. The target materials display enantiotropic smectic A phases with melting points and transition temperatures that are significantly higher than their phenyl analogues. The synthesis and mesomorphic behaviour of these new materials is reported and discussed.

Transannular aldol condensations within macrocyclic lactones: A novel approach to 8-membered carbocyclic rings.

Abstract A novel method has been developed for the construction of 8-membered carbocyclic rings, involving as the key step a chemoselective transannular aldol condensation within an 11-membered ketolactone ring.

Transannular vs Intramolecular Insertion Reactions of Transition Metal Carbenes: Evaluation of a Transannular Approach to Cyclooctane Ring Synthesis

Abstract The efficacy of closing cyclooctane rings via transannular metal-stabilized carbene insertion reactions within an 11-membered macrocyclic lactone ring was explored. The impact of performing these reactions in a transannular fashion was evaluated via a comparative study of closely analogous intramolecular (but not transannular) processes. Closure of a γ-lactone ring via intramolecular cyclopropanation on a moderately electron-deficient alkene proceeded in good yield under Cu(acac)2 catalysis, whereas analogous transannular cyclopropanation was thwarted by competitive β-hydride migration. In contrast, use of a more electron-rich methoxy-substituted alkene resulted in successful transannular cyclopropanation to afford the desired cyclooctane ring-containing product.

2-Alkoxy-1,3-thiazoles: A new core unit for incorporation into self-organising materials. Synthetic approach, mesomorphism, and electrooptic evaluation

The synthesis and transition temperatures of the first series of 2-alkoxy-1,3-thiazole-based liquid crystals are reported. The 2-alkoxy-1,3-thiazole moiety was generated in high yield via a selective SNAr reaction between 2,5-dibromo-1,3-thiazole and the corresponding long-chain alkoxide. The synthesis and mesomorphic properties of the aforementioned chevron-free 2-alkoxy-1,3-thiazole-based liquid crystals are discussed and compared with their 5-alkoxy-1,3-thiazole and phenyl based analogues. Electrooptical properties for both series of alkoxy-1,3-thiazole-based liquid crystals are also presented and discussed.