Thiocarbonyl isocyanates

Thioxo-1,2,4-dithiazolidines can be obtained from thioxo-l,2,4-thiadiazolidines by Dimroth rearrangement (Scheme 47) or reversibly by addition and elimination of acetone (Scheme 22). 1,2,4-Dithiazole type products are also obtained from thiocarbonyl isothiocyanates (154) by reaction with CI2 <84CHEC-I(6)897>, PhMgBr, Sj, or CS2. Other routes include reactions of carbonyl isothiocyanates and thiocarbonyl isocyanates with P4S10 or Sg <84Chec-I(6)897> and sulfonyl isocyanates with dialkyl thioketenes. Phenylisothiocyanate heated with N,C-disubstituted oxaziridines affords 3,5-diimino-l,2,4-dithiazolidines (226, 227). Other miscellaneous syntheses of 1,2,4-dithiazoline derivatives include cyclization of A7-thioacyl hexafluoroacetonimine to 5,5-bis(trifluoromethyl)-... 

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. " ... 

Two quite specific methods have been employed for the synthesis of imidazo[2,l- ]-[l,3,5]thiadiazines. In the condensation of l,2-diphenylimidazoline-4,5-dione (726) with a thiocarbonyl isocyanate such as (727), the isocyanate added to (726) in the manner of a Diels-Alder diene to produce (728) (67CB2064). 

A-1,3,5-Thiadiazines are prepared readily by (4-1-2) cycloaddition of A-thioacylimines with carbonitriles or cyanamides (see Section 6.18.10.2.2.iii). Analogous cycloadditions with alkoxy-thiocarbonyl isocyanates produce 2//-l,3,5-thiadiazine-4(3//)-thiones (see Section 6.18.10.2.2.iii). The boron-trifluoride etherate-catalyzed condensation of an aldehyde (or dialkyl ketone), a carbonitrile and a thioamide is also a versatile route to 4//-l,3,5-thiadiazines (see Section 6.18.10.3.2.2). 

Ethoxy(thiocarbonyl)isocyanate (367) undergoes [4+2] cycloaddition with aldehydes and ketones to give 1,3,5-oxathiazinones (383). 

Thiocarbonyl isocyanates react similarly with isonitriles to give 5-iminothiazolinone derivatives. ... 

Standing of the carbamoyl isothiocyanate 476 causes isomerization to the thiocarbonyl isocyanate 477, which undergoes dimerization to give the [4+2] cyclodimer 478 ° . 

Dithiolane isocyanate iminium methylides (55), are a new type of azomethine methylide derived 1,3-dipole, and undergo efficient and regioselective cycloaddition to thiocarbonyls to yield predominandy thiazolidine-2-thiones (56) <96TL711>. 

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. 

Metal-Oxygen Compounds. Trialkyltin alkoxides are remarkable for the variety of addition reactions they undergo with carbonyl and thiocarbonyl compounds. Bloodworth and Davies have reported reactions of tri-w-butyltin alkoxides with isocyanates, carbon dioxide, sulfur dioxide, isothiocyanates, carbon bisulfide, chloral, and ketene. The reactions observed were as follows ... 

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). 

In the absence of dipolarophiles the intermediate loses sulfur to give the carbodiimide however, the intermediate may be trapped with a number of alkenes, heterocumulenes and other reagents such as ynamines, ketenes, isocyanates, isothiocyanates, carbodiimides, ketenimines, sulfonylimines, imines, nitriles, thiocarbonyl compounds, Wittig reagents and the already mentioned enamines (80AG277). Contemporary knowledge of the chemistry of these sulfonyliminothiatriazolines is mainly due to the meticulous work of L abbe and his coworkers (80AG277). 

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... 

Few reactions of alkynes with C—X bonds are valuable for the preparation of four-membered hetero-cycles. Ynatnines react with aldehydes and ketones in the presence of Lewis acids to give unstable oxetene derivatives which undergo electrocyclic opening (Scheme 43). Open-chain products are also obtained with thiocarbonyl compounds,Schiff bases and iminium salts. Reactions of ynamines with carbon dioxide, ketenes, - ketenimines and isocyanates " often give mixtures of products and are of little preparative value. 

Treatment of TV.A -disubstituted thioureas with phosgene yields 4-imino-l,3-thiazetidine-2-ones (e-g-, 465 466 ). Thermolysis of esters 467 yields the thiazetidinones 468, and a 1,3-thiazetidinone 470 has been suggested as an intermediate in the photolysis of 469. l,3-Thiazetidine-2-ones are obtained by cycloaddition of phenylsulfonyl isocyanate to the thiocarbonyl groups of a thioamide. ... 

There are two methods for synthesizing this system in spite of the fact that it is the newest of the oxathiazines (i) cyclocondensation of 5-[/ -(hydroxyimino)alkyl]dithiocarbonates using tosyl isocyanate (Equation (21)), and (ii) cycloaddition of a-nitrosoalkenes to thiocarbonyl compounds (Equations (31) and (32)). The scope of method (i) is limited and gives only moderate yields. Method (ii) on the other hand is high yielding and preparation of the a-nitrosoalkenes is more straightforward than that of the six-atom fragment in (i). 

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