[1120-56-5] · C5H8 · Methylenecyclobutane · (MW 68.13)
(synthesis of 1-methylcyclobutene, cyclobutanone, and cyclopentanone)
Physical Data: bp 42 °C; n
Form Supplied in: usually available in ampules because of volatility.
Preparative Methods: may be prepared in 70% yield by Zinc reduction of pentaerythritol tetrabromide.1 Typical impurities in samples prepared by this method are 2-methyl-1-butene and spirocyclopropane. An alternative synthesis is available via methylenation of Cyclobutanone.2
Purification: NMR spectroscopy is the best method for determination of purity unless a GC equipped for determination of quite volatile materials is readily available.
Handling, Storage, and Precautions: use in a fume hood.
Methylenecyclobutane is used to prepare 1-methylcyclobutene by base-catalyzed double bond isomerization.3 A useful allyllithium reagent may be prepared from methylenecyclobutane via n-Butyllithium/N,N,N´,N´-Tetramethylethylenediamine mediated metalation (eq 1).4,5 Reaction of the cyclobutenylmethyllithium anion with electrophiles gives mixtures of regioisomeric products. In some cases the major cyclobutene products may be thermolyzed to give 2-substituted 1,3-butadienes.4,5
Methylenecyclobutane has also been used to prepare cyclobutanone2 by ozonolysis (eq 2) and cyclopentanone6 by ring expansion (eq 3).
Stephen R. Wilson
New York University, NY, USA