Thiocarbonic groups

Tetracyclic or tricyclic cyclobutyl ketones with an iodide or a thiocarbonate group in the a-position of the 3-substituent give tricyclic or spirocyclohexanones on treatment with tributyltin hydride. 

The dipole moments of three asymmetric polythiocarbonates derived from bisphenol A are determined in benzene solution at 298 K. Good agreement between theoretical and experimental results can be obtained assuming that the direction of the dipole moment of the thiocarbonate group Is opposite to that in carbonate residues. 

When cysteine reacts with an alkyl or aiyl chloroformate, both the —SH and —NH groups are protected as a thiocarbonate and as a carbamate, respectively. Selective or simultaneous removal of the protective groups is possible. 

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... 

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... 

S -Alkyl thiocarbamates (Table 4.24) have been synthesized [I] by a procedure (Scheme 4.19) which is closely analogous to that employed for the preparation of S-alkyl thiocarbonates (see Section 4.1), S-Glycosyl dithiocarbamates [2], which are useful precursors for thiosugars, have been prepared by simple nucleophilic displacement of the tosyloxy group by the N,N-diethyldithiocarbamate anion (cf preparation of S-glycosyl dithiocarbonates, 4.1.13). 

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). ... 

A radical cyclization has been achieved from a 1,3-dioxolanyl-thiocarbonate containing an alkyne group in an appropriate position (Equation 49) <2003TA2961>. The stereocontrol between cis- and trans-ivscd tricycles was 1.5-4.2 1. The products were similar to those depicted in Equation (36). 

An alternative method for formation of trisulfides1 0 has been derived from well-known procedures for the formation of disulfides that involve sulfenyl thiocarbonates as protecting/ activating groups for cysteine 25 In analogy to the chemistry for disulfides, cysteine side chains were protected and activated as extra-sulfur analogues, i.e. as S-(methoxy-carbonyl)disulfanyl or S-(/V-methyl-/V-phenylcarbamoyl)disulfanyl derivatives 10 Preferably,... 

In the alditol series, examples of acetobrominolysis of O-isopropyl-idene groups of derivatives of D-mannitol and D-iditol were given by McCasland and coworkers.i . i i Thus, the D-mannitol trithioearbonate derivative 157 gave the 1,6-dibromo derivative 158 (yield 55%).160 The same bromation with ring-opening was described for the D-iditol tri-thiocarbonate analog (yield 77%). 

Thiolcarbonic Acid, HS.CO.OH, yields carbon oxysulphide, COS, by decomposition its esters yield alcohols or mereaptans when saponified, according to whether the alkyl group is attached to oxygen or to sulphur by this means the constitutions of the thiocarbonic acids are established. 

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

The substituted ferrocenes 757 are widely used as metal-ligand systems. These compounds have a great variety of chelating groups (R) (1-diketones (a) [458], semicarbazones and thiosemicarbazones (b) [458], azomethines and their analogues (c) [458-462], oximes (d), carbonic, thiocarbonic (e), and amino acids (f) [458] ... 

Summary In this chapter, a discussion of the viscoelastic properties of selected polymeric materials is performed. The basic concepts of viscoelasticity, dealing with the fact that polymers above glass-transition temperature exhibit high entropic elasticity, are described at beginner level. The analysis of stress-strain for some polymeric materials is shortly described. Dielectric and dynamic mechanical behavior of aliphatic, cyclic saturated and aromatic substituted poly(methacrylate)s is well explained. An interesting approach of the relaxational processes is presented under the experience of the authors in these polymeric systems. The viscoelastic behavior of poly(itaconate)s with mono- and disubstitutions and the effect of the substituents and the functional groups is extensively discussed. The behavior of viscoelastic behavior of different poly(thiocarbonate)s is also analyzed. 

Keywords Viscoelasticity Glass transition temperature Relaxational processes Dielectric behavior Dynamic mechanical behavior Poly(methacrylate)s Poly (itaconate)s Poly(thiocarbonate)s Spacer groups Side chains Molecular motions... 

As a general example of another systems that show interesting responses from relaxational point of view, condensation polymers like poly(carbonate)s and poly (thiocarbonate)s are a new group of polymers to be analyzed. Poly(thiocarbonate)s... 

Both Bu3SnH and (Me3Si)3SiH are able to reduce alkyl iodides or bromides but not alcohols. However, in the Barton-McCombie reaction, they reduce certain alcohol derivatives, namely, ones that contain a C=S double bond (e. g., thiocarboxylic esters or thiocarbonic esters). Figure 1.39 shows how the OH group of cholesterol can he removed by means of a Barton-McCombie reaction. The C=S-containing alcohol derivative used there is a xanthate. 

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