Isothiocyanates, aryl-, cycloaddition

Cycloaddition of 2-nitrosopyridine 48 with nitrile oxides can give either di-A -oxides such as 49 or 3-mono-A -oxides such as 50 (93JHC287). In general, greater electron withdrawing character in the aromatic substituent appears to favor formation of the di-A -oxides. Sulfur ylides such as compound 51 are obtained from aryl isothiocyanates and l-amino-2-methylthiopyridinium iodides (84JCS(P1)1891) nitrogen ylides can be obtained from a similar reaction (86H(24)3363). 

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. ... 

The equilibrium between isothiocyanates and carbodiimides has been determined. The cycloaddition is favored by 59 to 79 kJ mol-1 with decomposition of the adduct being facilitated by electron donating groups on the aryl isothiocyanates (75JCS(P2)1475). Steric factors have also been shown to control the mode of addition and decomposition of isothiocyanates and carbodiimides (72JA3484). 

A cycloreversion mechanism is suggested for the transformation of the nonisolable cycloadduct 90 to the aldehyde 91 and isothiocyanate 92 <1996BCJ719> and for the spiro-1,4,2-oxathiazole intermediates 94 to the dioxothiazoline 95 and the aryl isothiocyanate 92 <2001MOL510>. Both cycloadducts are obtained by cycloaddition reactions of nitrile oxides 88 to thiocarbonyl compounds (Scheme 12). 

A representative 1,3-dipolar cycloaddition process occurs with yV-aryl-C-(trifiuoromethyl)-nitrilimines, generated from the corresponding hydrazonoyl bromides, c.g. 4. under basic conditions. which can react with dimethyl fumarate and maleate,bicyclic olefins. and dipolarophiles containing cumulative double bonds. With sodium isocyanates as the dipolarophilc the cycloaddition reaction occurs across the C = N bond, while with potassium isothiocyanate it occurs through the C = S bond. ... 

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... 

Reaction of l-benzyl-4-acetylimino-l,2,4-triazolium (493) with aryl isothiocyanates in benzene yields a mixture of 1,3-cycloaddition product (494) and 1,5-disubstituted triazole (495). However, in DMF, mainly the... 

With aryl isothiocyanates, 4-XCgH4NCS, (X = H, Me, OMe or NO2), complex 25a reacted in the familiar way by cycloaddition of the C=S bond and isocyanide insertion to form the bicyclo[2.2.2] adducts 32. The structure of 32, X = H, has been determined by X-ray crystallography. In the presence of a second equivalent of isocyanide, the bicyclo[3.2.2] products 33, resulting from a second isocyanide insertion, could be isolated. This reaction is cleanly thermally... 

Type H Syntheses of Thiazoles (S—C + C-N-C). Base-induced cycloadditions of tosylmethyl isocyanide (4-MeC6H4S02CH2NC) and an isothiocyanate RNCS (R = alkyl, allyl, PhCO, aryl, etc.) have been investigated. Depending on the reaction conditions, thiazoles (91) and/or imidazoles (92) are obtained. A high-yield ring-transformation of (91) to (92) occurs in THF/ BuLi. ... 

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