[1120-56-5]  · C5H8  · Methylenecyclobutane  · (MW 68.13)

(synthesis of 1-methylcyclobutene, cyclobutanone, and cyclopentanone)

Physical Data: bp 42 °C; n20D 1.4210.

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).

Related Reagents.

Cyclobutanone; Methylenecyclopropane; Squaric Acid; Tricarbonyl(cyclobutadiene)iron.

1. Roberts, J. D.; Sauer, C. W. JACS 1949, 71, 3925.
2. Fitjer, L.; Quabeck, U. S 1987, 299.
3. Shabtai, J.; Gil-Av, E. JOC 1963, 28, 2893.
4. Wilson, S. R.; Phillips, L. R. TL 1975, 3047.
5. Wilson, S. R.; Phillips, L. R.; Natalie, Jr., K. J. JACS 1979, 101, 3340.
6. McMurry, J. E.; Coppolino, A. P. JOC 1973, 38, 2821.

Stephen R. Wilson

New York University, NY, USA

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