Acylisocyanates, reactions

Acylisocyanates or isothiocyanates undergo cycloaddition with 5-hydroxy-THISs under so mild conditions that isolation of the initial adducts becomes possible (23). In cycloaddition reactions the 5-hydroxy-THISs can be replaced by their precursors (23). 

Of the new methods of preparation of oxo derivatives of the 5,6-dihydro-4//-1,3-oxazines, the most important is that developed by Martin and co-workers 169 the reaction of acylisocyanates with enol ethers at room temperature under nitrogen yields 48 [Eq. (35)] (see also Arbuzov et a/.170-171) together with an isomeric azetidinone. The... 

By reacting an acylisocyanate with dimethylketene, 4,6-dioxo derivatives of 1,3-oxazine (49) were obtained172 [Eq. (36)]. The reaction is exothermic and the temperature was kept below 40°C. 

Amide—> Isocyanate. A general procedure for the conversion of amides into acylisocyanates" provides a route to these compounds more convenient than the reaction of acid chlorides with silver cyanate. In the example formulated a mixture of u-chloroucelamide ami 100 ml. of ethylene dichloride is chilled to about 2" and timiH u/hiia D.6 mala of oxalvl uhlorldo li added all at on c. The mixture I removed... 

During the past twelve months a number of new phosphonium betaines and zwitterions has been reported. Reaction of ylides with acylisocyanates or acylisothiocyanates in methanol proceeds via a cyclization yielding pyrimidine substituted triphenylphosphonium salts (5) which can be converted into the corresponding betaines. The crystal structures of triphenylphosphonium-car-boxylate betaines 6 and 7 have been reported. Betaines 6 and 7 were obtained... 

Hetero-l-oxabutadiene systems that have been shown to participate as 47t components of Diels-Alder reactions include vinylnitroso compounds (31, 2-aza-l-oxabutadiene, Chapter 9, Section 3), fV-acylimines (32) as well as aromatic and aliphatic acylisocyanates (33, X = O) and isothiocyanates (33, X = S, 3-aza-l-oxabutadiene, Chapter 9, Section 3), acylnitroso compounds (34,2-aza-l, 4-dioxabutadiene, Chapter 9, Section 3), selected 4-aza-l-oxabutadienes, e.g., 35, including o-quinone monoimines (36,... 

This is in contrast to the reaction of acylisocyanates(RCONCO) with these substrates which as a result of [2+2] cycloaddition followed by loss of carbon dioxide yield acylimines (384). 

A suspension of Ag-cyanate in 5 parts petroleum ether treated dropwise with acetyl chloride, refluxed 1-2 hrs., the resulting AgCl removed by filtration, the filtrate containing acyl isocyanate treated with ethyl carbamate, and refluxed 4-6 hrs. ethyl 4-acetylallophanate. Y 70-90%. F. e. s. S. Umemoto and H. Takamatsu, Yakugaku Zasshi 88, 917 (1963) G. A. 60, 2815b f. reactions of acylisocyanates s. R. Neidlein, Arch. Pharm. 297, 623 (1964) 298, 124 (1965). 

Six-membered Rings.—Diels-Alder cyclizations using heterodienophiles provide a useful route to 1,2-thiazine derivatives immonium salts (300) derived from 7V-sulphinylmethylamine react across the N=S grouping. 1,3-Thiazinones are prepared " by reaction of thia-acylisocyanates (301) with enamines and enol ethers, and the formation of this ring system is also possible by reaction of JV-monosubstituted dithiocarbamates with a,/8-unsaturated acid chlorides. The reaction involves a series of equilibria, N- to S-transacylation, and cyclization reactions. 

Diphenyl phosphorochloridite allowed to react with 25%-excess isocyanic acid (prepared by cracking isocyanuric acid at 600 ) in ether in the presence of trimethylamine diphenyl phosphoro (isocyanatidite). Y 70%. F. e. and reactions, such as prepn. of acylisocyanates from carboxylic acid chlorides in pyridine, s. P. R. Steyermark, J. Org. Chem. 28, 586 (1963). 

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