Phenyl-thiocarbonyl isocyanate

Phenylthiocarbonyl isocyanate reacts similarly with carbodiimides to give [2+4] cycloadducts 217. From N-phenyl-N -cyclohexylcarbodiimide and phenyl-thiocarbonyl isocyanate two isomeric [2+4] cycloadducts are obtained. Aliphatic thiocarbonyl isocyanates react similarly to give [2+4] cycloadducts. " ... 

Intramolecular [3- -2]-cycloadditions of thiocarbonyl ylides with nonactivated acetylenes have also been described. Most representative examples involved the use of mesoionic substrates. The initially formed polycyclic adducts of type 110 undergo spontaneous elimination of phenyl isocyanate (24,62,151). A typical example leading to compound 111 is shown in Scheme 5.40. 

When acrylonitrile or ethyl acrylate was used as the dipolarophile, the azomethine adducts (134) and (135) were formed no thiocarbonyl ylide addition products were isolable in refluxing toluene or xylene, although the isoindoles (136a) and (136b) derived from them were isolated. In contrast to the reactions with fumaronitrile or AT-phenylmaleimide, the azomethine adducts (134) and (135) were still present at higher reaction temperatures — almost 50% in toluene and 4-5% in xylene. Under the same reaction conditions other electron-deficient dipolarophiles like dimethyl fumarate, norbornene, dimethyl maleate, phenyl isocyanate, phenyl isothiocyanate, benzoyl isothiocyanate, p-tosyl isocyanate and diphenylcyclopropenone failed to undergo cycloaddition to thienopyrrole (13), presumably due to steric interactions (77HC(30)317). 

Reaction of /i//yt/w-2-aryl-4-hydroxy-3-phenylthiazolium hydroxide (427) with isothiocyanates or isocyanates in hot benzene gives a crystalline cycloadduct for which the structure hexahydro-1,4-epithiopyrimidin-3-oxo-5-thiones/ones (428) was assigned on the basis of spectral data (76JOC8I3) in preference to hexahydro-1,4-pithiopyrazin-3-oxo-6-thi-ones/ones (429) and ylide structure (430) (Scheme 98). The IR spectrum of the cycloadduct is devoid of OH, SH, or NH absorption but shows the carbonyl and thiocarbonyl absorption. The H-NMR spectrum of the cycloadduct. obtained from 427a and phenyl isothiocyanate, is very simple. It consists of 15 aromatic protons at d 7.63 and a singlet proton at d 12.06 these are exceptionally low field. In the cycloadduct from 427a and phenyl... 

The reaction of isocyanates across C=S, N=0, S=0 and S=N bonds affords exchange products. For example, reaction of thiocarbonyl compounds with phenyl isocyanate at elevated temperatures affords azomethines and COS . This reaction most likely proceeds via the unstable [2+2] cycloadduct 167. 

In contrast to isocyanates, isothiocyanates reacted with 1,6-diynes at their C=S double bonds [57,68], As summarized in Table 3.15, Al-aryl, Al-alkyl, and Al-acyl isothiocyanates (1.2 equiv) underwent cycloaddition with a malonate-derived 1,6-diyne using 10 mol % of 6 in refluxing DCE to afford thiopyran imines 85 in 50 to 88% yields (entries 1 to 4). Increased amounts of isothiocyanates were detrimental, presumably due to the strong coordination of the soft thiocarbonyl moiety impairing access of the diyne substrate. Diyne substrates with quaternary carbon centers in their tethers were also required for successful cycloaddition with isothiocyanates. Moderate regioselectivity of 86/87 = 9 1 was observed for the cycloaddition of a malonate-derived unsymmetrical diyne with A/-phenyl isothiocyanate (Scheme 3.18). Upon treatment of a malonate-derived diyne with 10 mol % of 6 in a mixed solvent of carbon disulfide and DCE at 90 °C, cycloaddition with CS2 at the C=S double bond occurred to deliver 2//-thiopyran-2-thione 88 in a moderate yield (Scheme 3.18). 

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