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