Ruthenium-catalyzed [2 + 2] cycloadditions of bicyclic alkenes with alkynyl phosphonates.J Org Chem. 2009 Aug 07; 74(15):5762-5.JO
Ruthenium-catalyzed [2 + 2] cycloadditions of bicyclic alkenes with alkynyl phosphonates were investigated. The phosphonate moieties were found to be compatible with the Ru-catalyzed cycloadditions giving the corresponding cyclobutene cycloadducts in low to excellent yield (up to 96%). Alkynyl phosphonates showed lower reactivity than other heteroatom-substituted alkynes such as alkynyl halides, ynamides, alkynyl sulfides, and alkynyl sulfones and required a higher reaction temperature and much longer reaction time.