No abstract

Dialkylketenes add to ethoxyacetylene to give 4,4-dialkyl-3-ethoxy-2-cyclobuten-l-ones and to l-buten-3-ynyl methyl ether to give 4,4-dialkyl-3-(2-methoxyvinyl)-2-cyclobuten-l-ones. Some new reactions of these cyclobutenones are described.

Dimethylketene adds readily to a variety of vinyl ethers to form 3-alkoxy-2,2-dimethylcyclobutanones. Higher dialkyl ketenes, which dimerize much more slowly than dimethylketene, can be forced into cycloaddition to the less reactive allyl ethers and vinyl esters.

Ketenes underwent cycloaddition reaction& with several different heterocumiilenes. Dialkylketenes and isocyanates gave malonimides, and diisocyanates gave bis(ma1onimides). Acyl isocyanates and ketenes generally underwent a 4 + 2 cycloaddition to give oxazinediones. Carbodiimides and ketenes gave azetidinones vza a 2 + 2 cycloaddition. Carbon dioxide and carbon disulfide, when catalyzed by triphenylphosphine, gave 2 + 2 + 2 cycloaddition products containing 2 equiv of dialkylketenes. A ketenimine and a dialkylketene gave as the major component a 2 + 2 + 2 cycloaddition product involving two ketenimine molecules and one dialkylketene molecule.Ketenes belong to a class of compounds known as heterocumulenes.2 The reactions of ketenes with themselves to form dimers or trimers are well documented. I n this paper we report our work on reactions of ketenes with other heterocumulenes.Isocyanates. -Staudinger reported that diphenylketene reacted with phenyl isocyanate a t 220" via a 1: 1 cycloaddition to+ give the malonimide 1 in low yield.3 Similar reactions of diphenylketene with methyl and cyclohexyl isocyanates have been r e p~r t e d .~ The adduct of pentamethyleneketene, generated in situ from the acid chloride, with phenyl isocyanate also has been reported.6The reaction of monomeric dialkylkeTenes with isocyanates to give malonimides'has not been reported. We found that, when butylethylketene was heated with phenyl isocyanate, 2-butyl-2-ethyl-N-phenylmalonimide (2b) was formed in 70% yield. Dimethylketene, in spite of its reactive nature, gave low yields of malonimides because the ketene dimerized rapidly. At 25", dimethylketene and phenyl isocyanate afforded 2,2dimethyl-N-phenylmalonimide (2a) in 10% yield; at 60°, the yield of 2a was 30%.(1) (a) Paper XI1 in this series:

2513 3:1. These materials were separated with an Aerograph Autoprep Model A-700 (Wilkens Instrument and Research) and identified by comparison of their infrared spectra with those of authentic compounds.Reduction of la with Lithium Aluminum Hydride.-A solution of 50 g. (0.36 mole) of la in 75 ml. of dry ether was added slowly to a stirred slurry of 9.5 g. (0.25 mole) of lithium aluminum hydride in 500 ml. of dry ether. The reaction temperature was controlled at 15-20°b y an ice bath. The reaction mixture was stirred for 1 hr. after the addition was complete. Water (10 ml.) was added slowly, followed by 8 ml. of 20% sodium hydroxide solution and an additional 36 ml. of water. The alumina was removed by filtration and washed several times with ether.