Phenyl isothiocyanate 4+2 cycloaddition reactions

Organometallic dithiocarbimates are also known. Thus, a diarylgermanium phenyldithiocarbimate, Tbt(Tip)GeS2C=N-Ph, was obtained from the kinetic-ally stabilized diarylgermylene Tbt(Tip)Ge in a reaction with phenyl isothiocyanate, via [2+2] cycloaddition of a diarylgermanethione [Tbt(Tip)Ge=S] intermediate, evidenced by electronic spectroscopy.425... 

A successful method for preparing 1,3-thiazetidines is the cycloaddition of carbodiimides with isocyanates. The cycloadduct 151 was derived by the interaction of carbodiimide 152 and tosyl isothiocyanate . Reaction of 152 with methyl or phenyl isothiocyanate preferentially leads to iminotriazine-thiones. Cycloaddition between aryl isothiocyanates and dicyclohexylcar-bodiimide produced 153. ... 

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). 

The [2+2] cycloaddition reactions of various 4-dialkylamino-3-butyn-2-ones with substituted phenyl isothiocyanates in refluxing tetrahydrofuran gave access to a series of thietimines 92a-j in poor to satisfactory yields (Table 6) <2001SL361>. As it may be concluded from Table 6, when diethylamine derivatives were replaced by dimethylamine... 

Under photochemical conditions several 1,4-dipoles reacted with alkenes, alkynes, phenyl isothiocyanate and carbon disulphide to afford, after iodobenzene expulsion, cyclic adducts in moderate to low yields. This drawback is offset by the fact that it is difficult to obtain some of these compounds through alternative methods. Table 10.6 are listed selected examples of cyclic compounds formed by this methodology. Formally, these reactions can be considered as 1,3-dipolar cycloadditions, in which the 1,3-dipole comes from the iodonium precursor after elimination of iodobenzene actually, they arise most probably through 6-membered intermediate iodanes. 

Cycloaddition of phenyl isothiocyanate (296) to pyridinium salts (295) produced imidazo[l,2-a]pyridine-2(3i/)-thiones (297) (77MI41001). Reaction of l-aryl-2-... 

Substituted phenyl isothiocyanates 1 react with (dialkylamino)carbonitriles 2 at 800 MPa to give Af" -aryl-iV, A -dialkylquinazoline-2,4-diamine salts 3 in good to moderate yields. Mechanistically, the reaction probably involves repeated cycloaddition-dectrocyclic ring opening in which carbamimidoyl isothiocyanates are formed as intermediates " (cf. p 57). 

Cycloaddition of phenyl isothiocyanate (296) to pyridinium salts (295) produced imidazo[l,2-a]pyridine-2(3//)-thiones (297) (77Ml4looi). Reaction of l-aryl-2-chloropyridin-6-ones with mono-A/ -substituted ethylenediamines provided dihy-droimidazo[l,2-a]pyridin-5-ones (79CPB1207). Another procedure involves the polyphos-phoric acid cyclization of 2-(2-hydroxyethyl)aminopyridines (76AJC1039). Treatment of certain /3-aminoacrylic esters (298) with benzenediazonium fluoroborate (299) resulted in... 

CSI also reacts with diaryl azines (83) to afford the bicyclic triazolotriazolones (84), which are probably formed by 1,3-dipolar cycloaddition of CSI (two equivalents) to the azine (Scheme 39). Phenyl isothiocyanate undergoes a similar 1,3-dipolar cycloaddition reaction with a diaryl azine (83) to give the adduct (85) (Scheme 40). The main difference is that phenyl isothiocyanate is much less reactive than CSI, and consequently the cycloaddition requires more drastic conditions, namely prolonged boiling in xylene. 

Heating the symmetrical tetraazathiapentalenes under reflux in the presence of phenyl-isothiocyanate or isocyanate results in a postulated retro-cycloaddition followed by a subsequent cycloaddition to give the unsymmetrical products as well as new symmetrical products shown in Scheme 23. It is noteworthy that in contrast to substituted phenyl isothiocyanates, alkyl isothiocyanates fail to give any new products in this reaction. Similarly, reactions with isocyanates give asymmetric tetraazathiapentalenes which cannot be synthesized easily by other methods <91JHC221>. 

Cycloaddition and cyclization routes were used to access certain 1,3-diazines. The 4+2 cycloaddition reaction of 4-(N-allyl-N-aryl)amino-l,3-diaza-l,3-butadienes with vinyl-, isopropenyl-, and chloroketene led to pyrimidinone-fused pyrimidinones <97T13841>. Cis-cyclopenta[d]pyrimidines were derived from cis-2-amino-l-cyclopentanecarboxylates by cyclization with KOCN and KSCN <97JHC1211>. 2-Thioxopyrido[3, 2 4,5]thieno[3,2-r/]pyrimidin-4(3//)-ones 19 were prepared by cyclocondensation of 2-carbethoxy-3-amino-4-phenyl-6-substituted-thieno[2,3-/)]pyridines and isothiocyanates <97JHC937>. Thiazolyl-benzimidazoles derived from 2-cyanomethyl-l//-benzimidazole and 2,3-dihydrothiazole-2-(3//)-thiones were cyclized to the corresponding thiazolo[4,5-r/]pyrimidines <97PHA346>. Reductive cyclization of 6-cyanomethyl-5-nitropyrimidines afforded 7-alkyl-5//-pyrrolo[3,2-r/]pyrimidines and 6-amino-7,7-dialkyl-7//-pyrrolo[3,2-rf]pyrimidines <97T391>. 7-Methyl-5-alkyl-2-vinyl-pyrazolo[3,4-r/]pyrimidine-4,6(5//,7//)-diones arose from cyclization and alkylation of... 

A convenient synthesis of 1,3,4-thiadiazolidines using that most versatile of reactions, the 1,3-dipolar cycloaddition, has been developed by Motoyoshiya et al Phenyl hydrazones of ketones react with phenyl isothiocyanate and with carbon disulphide to give five-membered cyclic products, although phenyl hydrazones of aldehydes sometimes fail to react in this way (Scheme 53). 

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