a highly 
 selective cascade reaction that allows the direct transformation of 
 dienallenes to spirocyclobutenes ( spiro[3.4]octenes ) as single diastereoisomers 
 has been developed . 
 the reaction involves formation of overall four 
 c  c bonds and proceeds via a palladium - catalyzed oxidative 
 transformation with insertion of olefin , olefin , and carbon monoxide . 
 under slightly different reaction conditions , an additional co insertion 
 takes place to give spiro[4.4]nonenes with formation of overall five 
 c  c bonds .