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
Drastische Ausbeutesteigerungen bei Cyclisierungen zu gespannten Heterocyclen mittlerer Ringgröße
作者:Andreas Ostrowicki、Fritz Vögtle
DOI:10.1055/s-1988-27787
日期:——
Dramatic Yield Increase in Cyclizations Leading to Strained Heterocycles of Medium Ring Size By careful choice of the cyclization conditions (solvent, concentration of cesium hydroxide, high dilution) several strained heterocyclic metacyclophanes could be obtained in dramatically increased yields. The favorable effect of cesium hydroxide on the yield was proven.
The new medium membered heterocycles (2c–i), additionally strained due to internal substituents, could be obtained after optimization of a simple one-step cyclisation reaction; the barrier of the restricted rotations of the phenyl ring in (2h) and of the t-butyl group in (2i) were measured; the X-ray, NMR, and CD data of the stable enantiomers of (2c–i) are compared with those of the less strained