Helical thiaza[2.2]metacyclophanes. Synthesis, structure, circular dichroism, absolute configuration

Abstract

A series of helical-chiral 1-thia-10-aza[2.2]metacyclophanes 2–11 with different substituents at the nitrogen atom and at the aromatic ring have been synthesised and their chiroptical properties examined. These new N-substituted phanes are more suitable for the investigation of structure-chiroptics relationships than the already characterised N-tosylated aza[2.2]phanes. Their absolute configuration can be derived by comparison with the known parent compound 1 with free NH in the bridge.

Chiral separations were achieved by HPLC, using a cellulose carbamate-coated, chiral column material. The secondary amine 1 has been derivatised at the nitrogen atom with various electrophiles. The X-ray structures of 1–4 give detailed information about deformation and distortion in the [2.2]metacyclophane skeleton. In the N-tosyl[2.2]metacyclophanes 8–11, containing stilbene chromophores, the UV absorption is shifted bathochromically. The disturbing influence of hte tosyl chromophore in the CD spectra can be accounted for by the separation of the stilbene transitions. The synthetic method used is demonstrated to be more generally applicable to strained secondary amines by preparing the first chiral and even more strained thiaza[2.2]orthometacyclophane 15.