 After ring closure the new triple bond is stereoselectively reduced with hydrogen and the Lindlar catalyst in order to obtain the "Z"-alkene (cyclic "E"-alkenes are available through the Birch reduction).An important driving force for this type of reaction is the expulsion of small gaseous molecules such as acetylene or 2-butyne.The same two-step procedure was used in the synthesis of the naturally occurring cyclophane turriane.