Preparation and structural properties of hydroxy- and alkoxy-[2.2.1]metacyclophanes

Abstract

The asymmetric 4a and symmetric conformers 4b of a trimethoxy[2.2.1]metacyclophane were isolated and the structures were established by ¹H NMR spectroscopy and X-ray crystallography. The trihydroxy[2.2.1]-5 and dihydroxy(methoxy)[2.2.1]metacyclophane 6 were obtained by demethylation of isomers 4a and 4b, respectively. Treatment of compound 5 with ethyl bromoacetate afforded only the tris(ethoxycarbonylmethoxy)[2.2.1]metacyclophane 7. On the other hand the bis(ethoxycarbonylmethoxy)(methoxy)[2.2.1]-8 and ethoxycarbonylmethoxy(hydroxy)(methoxy)[2.2.1]metacyclophane 9 were obtained from compound 6. It was found that compounds 4a and 7 assume a ‘2,1-alternate’ conformation, whereas, on the other hand, compounds 4b, 6, 8 and 9 have a ‘2,2-alternate’ conformation. In the case of compound 5 both ‘2,1-alternate’ and ‘2,2-alternate’ conformers were detected by ¹H NMR spectroscopy. The chiralities of compounds 4a and 9 were confirmed by their ¹H NMR spectrum in the presence of Pirkle's reagent.