Directedorthoand Remote Metalation–Suzuki–Miyaura Cross Coupling Route to Azafluorenol Core Liquid Crystals

Abstract

Two new smectic C* mesogens containing a hexyloxy side chain and an azafluorenone (3a) or azafluorenol (3b) core were synthesized using a combined directed ortho metalation-directed remote metalation–Suzuki–Miyaura cross-coupling strategy. 3b was formed in 10 steps and 25% overall yield based on starting benzamide 1a. 3a forms a nematic phase, while 3b forms a smectic A phase. The large temperature range of the smectic phase for the azafluorenol 3b is indicative of mesophase stabilization by intermolecular hydrogen bonding between the hydroxyl group and pyridine nitrogen of neighboring 3b molecules.

Construction of an Axially Chiral Fluorene Nitrile-Based Framework via Benzannulation of Indene Diene with Benzoylacetonitrile

“…However, most of the reported innovative approaches are mainly focused on the construction of six-membered (hetero)­aryl–aryl, five-membered (hetero)­aryl–aryl, and others (Scheme a). In sharp contrast, the catalytic synthesis of fluorene-based atropisomeric frameworks has rarely been achieved, even though the fluorene-based axially chiral scaffolds are also ubiquitous in many natural products and pharmaceuticals as the core structures and easily modified for their distinctive structural characteristic. , That is because there are specific challenges involved in the catalytic synthesis of axially chiral fluorene-based frameworks (Scheme b), for example, the selection of suitable reactive substrates to construct fluorene without using preinstalled substrates, introduction of a hindered group to generate hindered rotation, and the choice of a competent organocatalyst to promote aromatization to construct fluorene and control the enantioselectivity. More importantly, few synthetic strategies are available for the catalytic synthesis of fluorene-based atropisomeric skeletons besides our previous strategies of benzannulation via a multistep cascade reaction of 1-indanylidene malononitrile with 3-benzylidenebenzofuran-2­(3 H )-one to access fluorenylamine-phenol atropisomers (Scheme c) …”