X-Ray crystal structures of 2,2′-bridged biphenyls with heterocyclic bridging rings: contraction in ring size on reduction

Abstract

X-Ray crystal structure analysis confirms that two of the four tetrabenzo [b,d,h,j][1,6]diazacyclododecines previously investigated have 12-membered rings; there is a strong presumption that the other two have a similar structure. Three of the four compounds undergo (dimethylamino)borane reduction to the tetrahydro derivatives in a process shown by X-Ray analysis and/or n.m.r. spectroscopy to involve C–N bond breaking and ring contraction from 12- to seven-membered rings. The fourth compound is shown by X-ray analysis to retain its (presumed) 12-membered ring structure when the tetrahydro derivative is produced by catalytic hydrogenation.