Isothiocyanates, addition carbon disulfide

Salts of dithiocarbamic acid can be prepared by the addition of primary or secondary amines to carbon disulfide. This reaction is similar to 16-9. Hydrogen sulfide can be eliminated from the product, directly or indirectly, to give isothiocyanates (RNCS). Isothiocyanates can be obtained directly by the reaction of primary amines and CS2 in pyridine in the presence of DCC. ° In the presence of diphenyl phosphite and pyridine, primary amines add to CO2 and to CS2 to give, respectively, symmetrically substituted ureas and thioureas ... 

Amidoximes (46) were first used as a source of 1,2,4-thiadiazoles in 1889 their condensation with carbon disulfide or with an excess of aryl isothiocyanate yields 3-aryl-5-mercapto- (47)6 -73 or 3-aryl-5-aryl-amino- 1,2,4-thiadiazoles (50),71,74,75 respectively. The latter reaction has been reexamined and discussed by Gheorgiu and Barbos76 who suggest that an initial addition of two moles of phenyl isothiocyanate to one of benzamidoxime is followed by cyclization of the intermediate (49), with elimination of phenylthiocarbamic acid (51). Decomposition of the latter gives rise to the by-products observed (cf. following scheme). 

This reaction may involve stepwise addition of the two equivalents of PhNCS via a 3-membered ring intermediate, RN—S—C=NPh.66 A thia-ziridine was also suggested by Borsche67 to explain the formation of 4-phenyl-5-phenylimino-l,2,4-dithiazolidine-3-thione from the aluminum chloride-catalyzed decomposition of phenyl azide in carbon disulfide. If a 4-substituted thiatriazoline is formed from phenyl isothiocyanate and the alkyl azide, the reaction may then be formulated as indicated in Eq. (21). This scheme is supported by the recent findings of Neidlein and... 

Fig. 8.11. Tandem reaction consisting of three single reactions mutually transforming heterocumulenes and heteroatom nucleophiles in a one-pot synthesis of an isothiocyanate (1) uncatalyzed addition reaction of heteroatom nucleophile (aniline) + heterocumulene (carbon disulfide) —> carbonic acid derivative (A) (2) heterolysis-initiated /3-elimination of the carbonic acid derivative (D) -> heterocumulene (F = phenylisothiocyanate) + heteroatom nucleophile (thiocar-bonic acid O-ethylester) (3) decomposition of a carbonic acid derivative (D) to a heterocumulene (carbon oxysulfide) and a heteroatom nucleophile (ethanol) via the zwitterion H.

Heterocyclic spirans are prepared by [Ni(CO)4]-promoted tandem cycloaddition of diphenylcyclopio-panone (100) to isothiocyanates (101 equation 43) or to carbon disulfide (105 equation 44). When an equimolar mixture of (100), (101) and [Ni(CO)4] is allowed to react in DMF at 65-70 C, two heterocyclic spirans, pyrrolin-2-one-5-spiro-5 -thiolen-4 -one (102), and (103), are formed in addition to the pyrroline derivative (104). Similarly, carbon disulfide (105), reacts with (100) to give thiolen-2-one-5-spiro-5 -thiolen-4 -one (106) along with a small amount of 1 1 cycloadduct (107). ... 

The adduct of Hector s base with carbon disulfide,1,3 first regarded as 21,37 has the solid state structure 22.40 With isothiocyanate esters, simple 5-thioureido derivatives (23, 24) are obtained (see also Refs. 35, 41). The structure of the addition compound with methyl isothiocyanate, for example, is 23 (R = Me) in both the crystalline and dissolved (DMSO) state, as determined by X-ray analysis, and 15N- and 13C-NMR measurements.31... 

To sum up, the addition of an unsaturated system X=Y=Z to Hector s base may be represented31,33 by the reaction sequence of Scheme 3, in which the final step involves merely a proton shift, and a rotation about a C—N bond. In the case of the isothiocyanate esters, factors as yet unknown terminate the reaction at the simple addition stage 25, but permit it to continue to 26 in the case of cyanamides and carbon disulfide. The dimethylated Hector s base does not form adducts with any of these reagents.31... 

In addition to activated olefins, other double-bond substrates, such as carbonyl and thiocarbonyl compounds and azomethines have been used ( ). Likewise, heterocumulenes, such as carbon disulfide, isocyanates, isothiocyanates, carbodiimides, and N-sulfinylamines have been added to nitrile imides ( ). While usually reaction occurs across one of the cumulative double bonds, with carbon disulfide only the bis-adduct LVIII could be isolated ( ). 

In the reaction of CpMn(CO)(CS)(C8Hi4) with carbon disulfide and PhsP as sulfur acceptor, di- and trithiocarbonyl complexes are obtained. Platinum and palladium [2-Fl] cycloadducts with CS2 and CSSe are also known In the reaction of oxaziridine with carbon disulfide, addition of the generated nitrene to carbon disulfide affords isothiocyanates and sulfur . 

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