y ne , ▁which ▁was ▁then ▁he ated ▁at ▁ 1 8 5   ° C ▁with ▁hydro ch lor ic ▁acid ▁for ▁ 1 0 ▁hours , ▁producing ▁a ▁mixture ▁of ▁ 2 - pro pen yl py rid ine ▁and ▁ 2 - ch lor op rop yl py rid ine . ▁This ▁mixture ▁was ▁reduced ▁to ▁rac - con i ine ▁by ▁sod ium ▁in ▁eth an ol . ▁ ▁[ The ▁final ▁structure ▁in ▁the ▁above ▁reaction ▁scheme ▁is ▁drawn ▁as ▁that ▁of ▁a ▁single ▁en anti omer , ▁although ▁the ▁final ▁reaction ▁produces ▁a ▁rac em ic ▁product .] ▁ ▁In ▁ 1 9 0 7 ▁the ▁process ▁was ▁still ▁further ▁improved ▁by ▁reducing ▁ 2 -( 2 '- h ydro xy pro py l ) py rid ine ▁with ▁ph osph orus ▁and ▁hydro iod ic ▁acid ▁at ▁ 1 2 5   ° C ▁and ▁tre ating ▁the ▁product ▁with ▁z inc ▁dust ▁and ▁water , ▁then ▁reducing ▁the ▁product ▁with ▁sod ium ▁in ▁eth an ol . ▁ ▁[ The ▁final ▁structure ▁in ▁the ▁above ▁reaction ▁scheme ▁is ▁drawn ▁as ▁that ▁of ▁a ▁single ▁en anti omer , ▁although ▁the ▁final ▁reaction ▁produces ▁a ▁rac em ic ▁product .] ▁ ▁A ▁number ▁of ▁other ▁synth eses ▁of ▁con i ine ▁have ▁been ▁effect ed , ▁of ▁which ▁that ▁of ▁D iels ▁and ▁Ald er ▁is ▁of ▁special ▁interest . ▁The ▁initial ▁ad duct ▁of ▁py rid ine ▁and ▁dim eth yl ▁ac ety len edic