Thiocarbonylations

The sulfur atom of the thiocarbonyl group is a good nucleophile, and reaction between benzyl bromide and l-(2-thiazolyl)thiourea yields the isothiouronium salt (496). The sulfur atom may also be engaged in a chelate, as exemplified by the Cu chelate of 2-thioureido-4-methylthiazole (491). These chelates with metal ions were thoroughly studied in acidic, neutral, and alkaline media for 66 metal ions in order to define their analytical use. They are formed in the molar ratio of 1 2 for metal II compounds (498). 

Steric overcrowding associated with the interaction betw een the thiocarbonyl group and a bulky alkyl group gives a bathochromic shift. This has been interpretated as evidence for a smaller thiocarbonyl group" in the first excited state (73). 

A recent report (62). using UNDO approximations, describes and interprets the phoioelectronic spectra of A-4-thiazoline-2-thione and other thiocarbonyl heterocycles. The results are given in Table VIl-3. The major feature is the clean separation between the two highest MOs and the others. The highest MO of tt symmetry 17.74 eV) is essentially localized on the dithiocarbamic part of the structure. The second one (8.12 eV) is highly localized on the exocyclic sulfur atom. This peculiaritv... 

Curiously enough, bulky substituents on nitrogen increase this reactivity towards methyl iodide (119). This has been related to a steric decompression of the thiocarbonyl group in the transition state. Furthermore, knowledge of the ratio of conformers in the starting 4-alkyl-3-i-Pr-A-4-thiazoline-2-thiones and in the resulting 4-alkyl-3-i-Pr-2-methylthiothi-azolium iodides combined with a Winstein-Holness treatment of the kinetic data indicates that in the transition state, the thiocarbonyl bond is approximately 65% along the reaction coordinate from the initial state... 

The effect of an o>-phenyl group as a function of the alkyl chain length has been studied in 3-(through-space interaction has been evidenced on the reactivity of the thiocarbonyl group. 

The rearrangement discovered by Kolosova et al. probably involves such reactivit (159). This reaction provides a good preparative method for various 5-amino-methylthiazoles (Scheme 43). No mechanism is proposed in the report, and it is not easy to understand how the C-5 enamine-like position competes with the very nucleophilic thiocarbonyl group of the formed A-4-thiazoline-2-thione. An alternative mechanism could start with ethanol addition at C-2. leading to the A-4-thiazoline (90) (Scheme 44). In this intermediate, C-5 nucleophilic reactivity would be favored bv the true enaminic structure. After alkylation on C-5,... 

Step 2 On reaction with hydrogen chloride m an anhydrous solvent the thiocarbonyl sulfur of the PTC derivative attacks the carbonyl carbon of the N terminal ammo acid The N terminal ammo acid is cleaved as a thiazolone derivative from the remainder of the peptide... 

The prefix thioxo- is used for naming =S in a thioketone. Sulfur analogs of acetals are named as alkylthio- or arylthio-. For example, CH3CH(SCH3)OCH3 is l-methoxy-l-(methylthio)ethane. Prefix forms for -carbothioic acids are hydroxy(thiocarbonyl)- when referring to the O-substituted acid and mercapto(carbonyl)- for the S-substituted acid. 

Radicals analogous to the above containing other chalcogens in place of oxygen are named by adding the prefixes thio-, seleno-, and so on for example, PS, thiophosphoryl CS, thiocarbonyl. 

Hydantoin derivatives show weak absorption in the uv-visible region, unless a part of the molecule other than the imidazohdinedione ring behaves as a chromophore (13) however, piC values have been determined by spectrophotometry in favorable cases (14). Absorption of uvby thiohydantoins is more intense, and the two bands observed have been attributed to n — tt and n — tr transitions of the thiocarbonyl group (15,16). Several piC values of thiohydantoins have been determined by uv-visible spectrophotometry (16). 

Cyclic Carhene Complexes. The reaction of aziridines with carbonyl, thiocarbonyl, or isonitrile ligands in Mn, Re, Fe, Ru, Pd, or Pt complexes leads to formation of cycHc carhene complexes (324—331). 

Physical Properties. Thiophosgene [463-71-8] (thiocarbonyl chloride), CSCI2, is a malodorous, red-yeUow Hquid (bp 73.5°C, ( 20 1.5442). It is only slightly soluble with decomposition in water, but it is soluble in ether and various organic solvents. 

If bromine is used in equation 8, carbon tetrabromide [558-13-4] is formed. With a minor amount of iodine present, and in the absence of iron catalyst, carbon disulfide and chlorine react to form trichioromethanesulfenyl chloride (perchloromethyl mercaptan [594-42-3]), CCI3SCI, which can be reduced with staimous chloride or tin, and hydrochloric acid to form thiophosgene (thiocarbonyl chloride [463-71-8], CSCI2, an intermediate in the synthesis of many organic compounds (see Sulfurcompounds). 

The mercapto form is much more strongly favored than is the hydroxy form for the corresponding oxygen compounds. A pertinent comparison in this respect is the greatly reduced inclination of enethiols to tautomerize to the corresponding thiocarbonyl compounds, in contrast to the facile ketonization of vinyl alcohols. 

Thermolysis of the 1,2,3-thiadiazoles (545) in the presence of carbon disulfide leads to the thiocarbonyl carbene (546) adduct, the ring-fused l,3-dithiole-2-thione (547) (76JOC730). 

Figure 8 Vectorially calculated dipole moments for the three planar conformations of l,l -thiocarbonyl-bis-...

Experimental and calculated (CNDO/S) vertical ionization energies have been measured for pyrazol-3-ine-5-thiones (108 R = H, Me). These compounds exhibit an intense low-energy band (7.55-7.60 eV) corresponding to the ionization of both a thiocarbonyl tt-electron and the sulfur n electron (78JA1275). 

The reaction of thiocarbonyl compounds with diazoalkanes (alkyl, aryl substituted) frequently gives good to excellent yields of thiiranes. The mechanism may involve addition of a carbene across the thiocarbonyl group, especially in the presence of rhodium(II) acetate... 

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