Chromium-Templated Synthesis of Densely Substituted Distorted Arenes − Intramolecular Benzannulation of [(Alkynylaryl)alkenyl]carbene Complexes to Planar-Chiral Hydroquinoid [2.2]Heterametacyclophanes

Abstract

{[(meta‐Alkynylphenyl)alkenyl]carbene}chromium compounds 1 and 2 have been synthesized by four‐step (or five‐step) and seven‐step sequences, starting from 3‐halophenol or 3‐haloaniline, respectively. This approach, involving high‐yielding Takai reactions and lithium cuprate additions, provides a novel and straightforward route to [(alkynylaryl)alkenyl](methoxy)carbene complexes. Upon gentle warming in tetrahydrofuran, (carbene)chromium compounds of this type undergo intramolecular benzannulation to give novel [2.2]heterametacyclophanes 21 and 22, bearing two chiral planes arising from the unsymmetrical substitution patterns both of the cyclophane skeleton and of the newly formed, Cr(CO)3‐coordinated benzohydroquinone deck.

Mass Spectrometric Detection and Fragmentation Patterns of Synthetically Useful Chromium and Tungsten Carbene Complexes

“…Chromium carbene complexes are well-known and widely used reagents for organic synthesis . They have been used for the synthesis of a number of natural products such as peptides, vitamins, antibiotics, steroids, and alkaloids as well as for the preparation of cyclophanes, dendritic molecules, and axial or helical chiral 6 frameworks. In these cases, readily accessible aryl- or vinylcarbene chromium complexes serve as starting materials for the [3 + 2 + 1]-benzannulation reaction with alkynes, providing a straightforward approach to densely functionalized benzenoids and fused arenes regioselectively labeled with a Cr(CO) 3 fragment.…”