Thioacyl isocyanates

Similarly to the dihydrooxazinones (Section II,A,5), the title compounds can be prepared by the cycloaddition of thioacyl isocyanates to cycloalkenes containing an activated C = C bond. 

The cycloadditions of thioacyl isocyanates proceeded with exo and cis selectivity. 

Dihydro- 1,3-oxazines (398) are cyclic intermediates in the synthesis of a-amino-y-oxo acid esters by reaction of acyliminoacetates with enamines derived from six-membered ketones240. Sulfur-containing heterocycloadducts 399 and 400 have been prepared by [4 + 2] cycloaddition of enamines to heterocumulenes like thioacyl isocyanates and acyl isothiocyanates241. 

Thioacyl isocyanates and acyl isocyanates O. Tsuge, Heterocycles, 1979,12, 1067. 

Thia-1-aza- N-Thioacylimines butadienes x = o,s Thioacyl isocyanates and N-Thioacyl dithioimidocaibonates... 

Amino-l, 3-thiazin-4-ones (245) (X = O), or thiones (245) (X = S), are obtainable via the cycloadditions of l-(A,A-diethylamino)propyne (246) and thioacyl isocyanates, or isothiocyanates, respectively (Equation (30)) <85ZC324>. A less common approach utilizes nitriles as the C—N component in [4 - - 2] constructions of l,3-thiazin-4-ones thus, the cyclization of the ( )-thiohemi-acetal (247) with (248) gives the 2-phenoxy-l,3-thiazin-4-one (249) (Equation (31)) <85ZC430>. 

Two strategies have appeared which afford this type of compound (i) cycloaddition of N-thioacylimines to ketones (Scheme 12), and (ii) cycloaddition of thioacyl isocyanates to ketones... 

Because of their predictable behavior and reactivity, thioacyl isocyanates comprise the bulk of this work, and extensive studies of their [4 + 2] reactions with olefins,83 enamines,84 enol ethers,843 thioacyl isocyanates,85 imines,85 1 86 carbodiimides,84387 isocyanates,843 azirines,88 /3-enaminoke-tones,89 dianils,86d azines,90 hydrazones,91 imidazoline-4,5-diones,92 aryl cyanates,93 disubstituted cyanamides,93 aldehydes,94 ketones,94 ketenes,94 alkyl or aryl iminodithiocarbonates,95 and the carbon-carbon double bond of ketenimines96 have been detailed. In an extensive comparative study of the [4 + 2] cycloaddition reactions of thioacyl isocyanates, the heterocu-mulenes bearing strong electron-withdrawing substituents were found to be more stable and less prone to participate in cycloaddition reactions.84 Representative examples are summarized in Scheme 9-IV. 

A wide range of 3-aza-l-thia-l,3-butadiene systems has been extensively investigated as Att components of Diels-Alder reactions. The work with each of these systems is summarized in Chapter 9 and includes the 477-Diels-Alder reactions of appropriately substituted TV-thioacylimines (e.g., 29, Chapter 9, Section 3),47-56 thioacyl isocyanates (e.g., 30, Chapter 9, Section 3),5758 thioacyl isothiocyanates (e.g., 31, Chapter 9, Section 3),5759 and TV-thioacyl dithioimidocarbonates (e.g., 32).2223 Examples of... 

S), thioacyl isocyanates (10, X = S, Y = O), or thioacyl isothiocyanates (10, X=Y=S) will participate in selected [4 + 2] cycloaddition reactions, and substantial differences in reactivity exist between these related he-tero-2-azadienes. Much of this work has been reviewed.7 71... 

Thioacyl isocyanates react with 2-bromoethanol to give urethanes (215), which generally react with base to give oxazolidinones (214) however, when R is t-butyl, the 1,5,3-oxathiazepinone (216) is obtained in 60% yield. 

Derivatives of Thioamides. (i) Syntheses,reactions, and physical properties of thiohydrazides. (ii) Syntheses and reactions of thio-hydroxamic acids. (iii) Syntheses, dimerization, trimerization, and reactions of thioacyl isocyanates. ... 

Thiazinediones 513 are constmcted in 78% yield when ketenes react with thioacyl isocyanates, as in the reaction of thiobenzoyl isocyanate with diphenylketene (Scheme 168) (1972CB3322). These reactions are performed in ether or aromatic solvents in the absence of additives and catalysts. The isolation of azetidinedione as by-products has been reported. 

A series of recent papers documents solid advance within the chemistry of thioacyl isocyanates. Thus a variety of heterocyclic compounds have been obtained in (4+2) cycloaddition reactions of thiobenzoyl isocyanate (276) with aldehydes, diarylketens, ketenimines, benzylideneamines, ... 

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