PtCl2-Catalyzed Rearrangement of Methylenecyclopropanes

• Published in: Journal of the American Chemical Society Vol. 128; no. 19; pp. 6306 - 6307
• Main Authors: Furstner, Alois, Aissa, Christophe
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 17.05.2006; Amer Chemical Soc
• Subjects: Chemistry; Chemistry, Multidisciplinary; Exact sciences and technology; Kinetics and mechanisms; Organic chemistry; Physical Sciences; Reactivity and mechanisms; Science & Technology; GOLD; PHENANTHRENES; DIENES; OLEFINATION; PT(II); ACIDS; CYCLIZATION; CATALYZED CYCLOISOMERIZATION REACTIONS; Chemical rearrangement; Platinum chloride; Catalytic reaction; Cyclopropane derivatives; Isotope effect; Transition metal Compounds; Reaction mechanism; NMR spectrometry; Experimental study; Catalyst activity; Catalyst; Monocyclic compound
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja061392y

Alkylidenecyclopropanes readily convert into cyclobutene derivatives on treatment with catalytic amounts of PtCl2. The reaction is strongly accelerated when performed under an atmosphere of CO (1 atm). The resulting cyclobutenes are isolated in good to excellent yields for substrates bearing aliphatic as well as aromatic substituents R on their olefinic site. If the substituent R, however, is a very electron-rich arene, the cyclobutenes initially formed react further to give dimeric products with a previously unknown 1,2,2a,7a-tetrahydrospiro[cyclobuta[a]indene-7,1‘-cyclobutane skeleton. A mechanism accounting for these experimental observations as well as for a deuterium-labeling experiment is proposed which implies reactive intermediates at the nonclassical cation/carbene interface. Furthermore it is shown that the PtCl2-catalyzed cyclobutene formation can be geared with subsequent ring-opening/ring-closing metathesis (ROM/RCM) events. Finally, a convenient “one pot” method for the preparation of the alkylidenecyclopropane substrates used in this study is presented, which is based on a modified Julia−Kocienski olefination of aldehydes with readily available 1-tert-butyl-1H-tetrazol-5-yl-cyclopropyl sulfone under Barbier conditions.