Thiocarbonates reactions

Thiophosgene reacts with alcohols and phenols to form chlorothionoformates or thiocarbonates. The most studied reactions of thiophosgene are with primary amines to give isothiocyanates and with secondary amines to give thiocarbamyl chlorides ... 

CH30C(0)SC1, 0-5°, 1.5 h r-BuSH, MeOH, 5 days, 97% crude, 46% pure. The reaction proceeds through an 5-sulfenyl thiocarbonate. 

A number of less-hazardous reagents that can be substituted for tert-hutyl azidoformate in tert-butoxycarbonylation reactions are available including 2-(te/t-butoxycarbonyloxyimino)-2-phenylacetonitrile (Aldrich Chemical Company), 0-teri-hutyl N-phenyl thiocarbonate (Eastman Organic Chemicals), di-butyl dicarbonate and tert-butyl phenyl carbonate. ... 

On reaction of the S/Z-mixture 746 with benzylamine in the presence of CS2, the cyclic thiocarbonates 757 and 758 are formed by attack of benzylammo-nium thiocarbonate on 747, N,N -thiourea 759 is also formed [236] (Scheme 5.81). 

The precise reaction conditions for optimal yields depend upon the specific reagents and both thermal290 and photochemical291 conditions have been developed. Phenyl thionocarbonates are easily prepared and are useful in radical generating reactions.292 A variety of other thiono esters, including xanthates and imidazolyl thiocarbonates also can be used.293... 

The asymmetric reduction of the benzoxathiin is very appealing because of its simplicity (Scheme 5.3). It was envisioned that intermediate 16 could be prepared from thiol-phenol 7 and bro moke tone 17. Scheme 5.8 summarized the synthesis for 16. The l,3-benzoxathiol-2-one 35 was prepared from 1,4-benzoquinone and thiourea following a literature procedure with minor modifications. Benzylation of 35 with benzyl bromide in the presence of KI gave benzyl ether 36 as a crystalline solid. It was observed that the benzylation gave better results when the reaction was run under anaerobic conditions. Hydrolysis of thiocarbonate 36 gave free thiophenol 7 which was used directly in the next reaction. 

Nitro-aldols, which are readily available (see Henry reaction Section 3.1), are converted into olefins via conversion of the hydroxyl group to the corresponding phenyl thiocarbonate ester and treatment with tin radical.158 The yield was not reported. Because the radical deoxygenation via thiocarbonate (Barton reaction) proceeds in good yield, the elimination of Eq. 7.115 might be good choice for olefin synthesis.159... 

Direct oxidation of thiocarbonyl compound by triflic anhydride results in stable dication salts containing disulfide framework. For example, reaction of thiocarbonate 155 with Tf2Q yields the dication salt 156 (Scheme 58).154... 

A fused OZT was obtained in the course of the reduction of vicinal azido-thiocarbonates via formation of the intermediate amine, which attacks the thiocarbonyl group (Scheme 37). The condensation reaction proved faster than the deoxygenation process for the synthesis of 2 -amino-2, 3 -dideoxyuridine50 or methyl 3-amino-4,6-0-benzylidene-3-deoxy-2-0-phenoxythiocarbonyl-a-L-talopyranoside.51... 

The reduction of thiocarbonyl derivatives by EtsSiH can be described as a chain process under forced conditions (Reaction 4.50) [89,90]. Indeed, in Reaction (4.51) for example, the reduction of phenyl thiocarbonate in EtsSiD as the solvent needed 1 equiv of dibenzoyl peroxide as initiator at 110 °C, and afforded the desired product in 91 % yield, where the deuterium incorporation was only 48% [90]. Nevertheless, there are some interesting applications for these less reactive silanes in radical chain reactions. For example, this method was used as an efficient deoxygenation step (Reaction 4.52) in the synthesis of 4,4-difluoroglutamine [91]. 1,2-Diols can also be transformed into olefins using the Barton-McCombie methodology. Reaction (4.53) shows the olefination procedure of a bis-xanthate using EtsSiH [89]. 

Thiocarbonates, synthesis of, 17, 3 Thiocyanation of aromatic amines, phenols, and polynuclear hydrocarbons, 3, 6 Thiophenes, synthesis of, 6, 9 Thorpe-Ziegler condensation, 15, 1 31 Tiemann reaction, 3, 9 Tiffeneau-Demjanov reaction, 11, 2 Tin(n) enolates, 46, 1 Tin hydride method to prepare radicals,... 

Because vicinal dibromides are usually made by bromination of alkenes, their utility for synthesis is limited, except for temporary masking of a double bond. Much more frequently, it is desirable to convert a diol to an alkene. Several useful procedures have been developed. The reductive deoxygenation of diols via thiocarbonates was developed by Corey and co-workers.210 Triethyl phosphite is useful for many cases, but the more reactive reductant l,3-dimethyl-2-phenyl-l,3,2-diazaphosphohdine can be used when milder conditions are required.211 The reaction presumably occurs by initial P—S bonding... 

F-17(20)-dehydro-20-cyanopregnene, which may be isomerized in base to the Z-isomer. Elaboration of the side-chain by successive Grignard reaction, reduction, and removal of the 22-hydroxy-group followed. Key steps in two stereospecific syntheses of Z-20(22)-dehydrocholesterol (234) from pregnenolone were (a) stereospecific removal of the 20- and 22-oxygen atoms of (20i ,22S)-20,22-dihydroxycholesterol by conversion into the thiocarbonate (232) and treatment with triethyl phosphite and (b) selective epoxidation of iE -20(22)-dehydrocholes-teryl benzoate to the epoxides (233), which were allowed to react with hexamcthyIdisilane-KOMe in HMPA (see also ref. 179). Syntheses of the 24-... 

Barton-McCombie deoxygenation is not always stereoselective the diastereo-meric ratios strongly depends on the nature of the protecting groups and of the ester moiety. However, in 2-C-trifluoromethyl-2-deoxyfuranose, the a compound is the major product of the reaction, due to steric hindrance of this a side. In 3-C-trifluoromethyl-3-deoxyfuranose, deoxygenation by tributyltin hydride yields only the a product, if it is performed with oxalate instead of thiocarbonate. Another possibility to obtain this selectivity is to perform the reaction with 1,2,5,6-di-O-isopropylidene-a-D-glucofuranose (Figure 6.34). ... 

Cyclic thiocarbonates, such as compound 169, react smoothly with allylmagnesium bromide. Careful control of the reaction conditions allows monoalkylation. Trapping of the intermediate sulfur anion with Mel provided the 1,3-dioxane in 78% yield (Equation 20) <2003H(59)87>. 

The reaction was further developed to form a wide range of p-lactam-based products (52). Treatment of the racemic ylide processor 186 with suitable sulfur-based thiocarboxylate or thiocarbonate dipolarophiles gave rise to the expected racemic penams 189 and 190 and penems as single regioisomers (Scheme 3.54). Once again, the use of the chiral dipolarophile 186 furnished the cycloaddition product 191 with complete enantiomeric integrity. Similarly, the use of aldehydes... 

Carbon disulphide interacts with dry ammonia, but the reaction has not yet been fully investigated the gas is slowly absorbed and a dark brown liquid results, which probably contains ammonium thiocarbonate and thiocyanate.6 An alcohol solution of ammonia readily dissolves carbon disulphide,7 the foregoing products being formed (see also p. 264).8... 

D. H. R. Barton and R. Subramanian, Reactions of relevance to the chemistry of aminoglycoside antibiotics. Part 7. Conversion of thiocarbonates into deoxy-sugars, J. Chem. Soc. Perkin Tram. 7 1718 (1977). 

The preparation of carbonates is mechanistically closely related to the synthesis of carbamates, and similar reagents can be used for this purpose (Table 14.10). Resin-bound alcohols can be directly converted into carbonates by treatment with a chloro-formate (see Experimental Procedure 14.2), in two steps by activation with phosgene or a synthetic equivalent thereof followed by reaction with an alcohol in the presence of a base, or by treatment of a resin-bound alcohol with carbon dioxide and an alkyl halide under basic reaction conditions [125]. Thiocarbonates can be prepared from... 

Thiocarbonate esters, obtained from aryl chlorothionoformates and hydroxyl groups, react similarly [206, 207]. This reaction was also used for the dehydration of oximes [208]. 

Tkiocarbonate. Potassium thiocarbonate, K2CS3, yellow solid, soluble, formed by reaction of potassium sulfide and CS2. 

The reaction of alkyl isothiocyanates, RNCS, with diphenylphosphinic hydrazide (338) in benzene has been reported.308 The bis(diethylamino)[(methylthio)thiocarbon-yl]carbenium salts (339 X = I or BF4) display ambident reactivity and can react either at carbenium carbon (hard nucleophiles) or at the thiocarbonyl sulfur atom (soft nucleophiles).309 Electrochemically generated superoxide reacts with dithioic S,S -diesters (dicarbothiolates) (340 Ar = C5H3N or C6H4) to give the monocarboxylate anions in 100% yield before giving the dicarboxylate anions.310... 

Carbonates as well as thiocarbonates, for example, (Ja)-120 <2004TL39>, (R)-248 <1999CL93>, and (R)-249 <1998JA4530>, were readily prepared by reaction of the corresponding diol with triphosgene and thiophosgene. 

Spiroorthocarbonates were obtained by coupling of cyclic tin adduct 251, prepared from 1,2-dihydroxymethyl-benzene and dibutyltin oxide, with thiocarbonate 252. Reaction of the resulting orthocarbonate 253 with potassium A/z-butoxide in toluene afforded spiroorthocarbonate 254 (Scheme 77) <2003BKC1371>. 

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