Selective thiocarbonylation

TABLE 26. Experimental determination of gas-phase basicities of selected thiocarbonyl and carbonyl compounds ... 

TABLE 18. Equilibrium constants A c (in lmol 1) for the formation of 1 1 CT complexes between I2 and selected thiocarbonyl compounds in n-heptane at 25.0 °C539... 

Site-selective deo>ygenation of biologically active polyols is an attractive transformation, which enables expansion of the structural diversity of the polyols and increases the opportunity to find biologically active analogues. Site-selective deojygenation of polyols was investigated by the sequence of site-selective thiocarbonylation and Barton-McCombie reaction. Site-selective thiocarbonylation of a-methyl glucoside 93 was examined with phenyl... 

Scheme 22.22 Site-selective thiocarbonylation/deoxygenation of sugar derivatives.

Scheme 22.23 Site-selective thiocarbonylation/deojygenation of vancomycin.

Fowler BS, Laemmerhold KM, Miller SJ (2012) Catalytic site-selective thiocarbonylations and deoxygenations of vancomycin reveal hydroxyl-dependent conformational effects. J Am Chem Soc 134 9755-9761... 

Scheme 5 Selective thiocarbonylation of a glucopyranoside-derived diol mediated by N-methylimidazole-bearing peptide catalysts. PEMP denotes 1,2,2,6,6-pentamethylpiperidine...

Table 38. Geometric parameters of the So, Si and S2 states of selected thiocarbonyl compounds.

Kawakami J, Mihara M, Kamiya I, Takeba M, Ogawa A, Sonoda N (2003) Platinum-catalyzed highly selective thiocarbonylation of acetyltaies with thiols and carbon monoxide. Tetrahedron 59 3521-3526... 

Perfluoropyridine gives the usual replacement of the 4-fluonne on reactions with either aromatic or aliphatic mercaptides [55, 36] The reaction of perfluoropyridine with cesium tnfluoromethyl mercaptide, generated from thiocarbonyl fluoride and cesium fluonde, shows temperature dependence of selectivity in fluonne displacement [55 36] (equation 24)... 

Although neither of the two carbonyl groups in 18 is immune to the action of Lawesson s reagent,11 it is possible to bring about the selective conversion of the more Lewis-basic lactam carbonyl to the corresponding thiocarbonyl. Thus, treatment of 18 with Lawesson s reagent results in the formation of thiolactam 19 in 85% overall yield from 13. 

Ethoxycarbonyl chloride is, by virtue of resonance involving the ester function, less reactive than acetyl chloride, and the reagent has found application for selective O-acylation in the steroid field.34 With this reagent, methyl 4,6-O-benzylidene-a-D-glucopyranoside yielded35 2- and 3-esters in the ratio 24 1, and the related benzyl-thiocarbonyl chloride gave the 2-ester in 58% yield.36... 

Methods for the A-acylation of similar heterocycles, such as simple thiazolidinethiones, have been reported since 1977, namely acyl chlorides in miscellaneous conditions,586 or carboxylic acids under DCC-activation.60,61 However the easiest and most effective method involves acyl chlorides or carboxylic anhydrides in the presence of an amine.47 Applying that procedure on carbohydrate scaffolds Rollin and co-workers62 reported the synthesis of diverse /V-acylated OZTs. The reactions were performed with good yields and the /V-selective acylation was ascertained by NMR— namely the thiocarbonyl 13C chemical shift (Scheme 41). Thanks to the dual nature of the carbanion drifting in the reaction,596 60 no competitive formation of the thioester, as mentioned by Plusquellec el al. in the case of benzothiazole, was observed. 

The 5-dig-mode of cyclization has been applied in the synthesis of N-heterocycles. For example, treatment of the /i-allenyl dithiosemicarbazide 37 with Bu3SnH and AIBN in hot benzene furnishes the substituted 3H-pyrrole 38 in 41% yield and the isomeric heterocycle 39 in 30% yield (Scheme 11.13) [68], Iminyl radical 40 is formed via Bu3Sn addition to the thiocarbonyl group of the radical precursor 37 and fragmentation of the adduct (not shown). Nitrogen-centered radical 40 adds 5-dig-selectively to provide substituted allyl radical 41. The latter intermediate is trapped by Bu3SnH to furnish preferentially product 38 with an endocydic double bond. 

Reactions involving sulfur-linked substituents have been exclusively dealkylations of S-alkyl substituents to yield a thiocarbonyl group. Debenzyl-ations under mild conditions with aluminum chloride in benzene were mentioned earlier (Section IV,A,2,a). Pyridine demethylates salts 137 selectively to give 175. ° ... 

Like other 1,3-dipolar species, thiocarbonyl ylides are able to enter intramolecular as well as intermolecular cycloaddition reactions. In this chapter, selected examples of both types will be illustrated. 

A-Sulfinylamines (R—N=S=0) are known to function as reactive dienophiles and dipolarophiles, and some examples of [3 + 2] cycloaddition with thiocarbonyl ylides have been reported (176). For example, the reaction of thiobenzophenone (5)-methylide (16) with both A-phenyl and N-tosylsulfinylamines occurs regiose-lectively to give 1,3,4-dithiazolidine 3-oxides (135). In the case of thiocarbonyl ylide 69, reaction with N-phenyl sulfinylamine selectively afforded the analogous product 136 (R = Ph). However, the corresponding reaction with Al-tosyl sulfinylamine resulted in a mixture of the N,S-adduct (136) (R =Tos) and the 0,S-adduct 137. Formation of a mixture of products is compatible with a stepwise reaction via a zwitterionic intermediate. 

The metal-catalyzed formation of 2,3-dihydrothiophene derivatives via a 1,5-dipolar electrocyclization has been reported by Hamaguchi et al. (124). For example, the Rh2(OAc)4-catalyzed reaction of vinyldiazo compound 159 (R = Ph) with xanthione (160) produced the spirocychc drhydrothiophene 161. In contrast, when 159 containing a methyl group (R = Me) was used, thiirane 162 was the sole product (Scheme 5.48). This result was rationalized by the selective formation of an intermediate thiocarbonyl yhde 163 with (Z)- and ( )-configuration, respectively. 

Karlsson and Hogberg (291,292) applied the thiocarbonyl ylide 175 in a diastereoselective 1,3-dipolar cycloaddition with 165. The thiocarbonyl yhde was generated in situ by an elimination reaction. The reaction with 165 gave 176 (R = Bu, BnO, Ph) with selectivities of up to 64—80% de. Furthermore, the cycloaddition of a chiral galactose-derived nitrile imine with 165 has been reported (104). 

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