This in turn is then ring closed by a stereospecific process of inversion with pyridine in {HEAD ~ p toluenesulfonyl chloride} to obtain {TAIL ~ dibenzofuran} 
to obtain
This in turn is then ring closed by a stereospecific process of inversion with pyridine in { HEAD ~ p toluenesulfonyl chloride } to obtain { TAIL ~ dibenzofuran }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL