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