Phosphorus-thiol group

The first overtone of the S-H group can be seen in Figure 9.1 as the weak peak near 5050 cm k The phosphorus-thiol group (P-SH) shows a shift from the normal thiol overtone and gives rise to a weak doublet at 5076-5002 cm (1970 and 1999 nm)." ... 

Sections I and J of Scheme 3.2 show reactions with sulfur and phosphorus nucleophiles. The reaction in Entry 25 is a useful method for introducing thiol groups. The solid thiourea is a convenient source of sulfur. A thiouronium ion is formed and this avoids competition from formation of a dialkyl sulfide. The intermediate is readily hydrolyzed by base. 

The only alkyl group reported as reductively removed is the di-phenylmethyl substituent from N3 in compound 165.153 Deoxygenation of N-oxides can be done thermally (heating in toluene with oxygen transfer to solvent) for compounds of type 166,44 or more commonly by use of phosphorus derivatives, as described for compounds 32, 33,45 166,44 and 167.61 Halogens can be reductively removed from [l,2,3]triazolo-[4,5-6]pyridines 160,146 168,220 and 169,142 and from pentachloro derivative 164, giving dichloro compound 170.208 Removal of thiol groups by reduction... 

Replacement of a hydroxy with a thiol group, using phosphorus penta-sulfide in refluxing pyridine, has been reported for pyrazolo[4,3-c]pyrid-4-(54-75%)144,146 and pyrazolo[3,4-c]pyrid-7-ones (67%). 10... 

In the total synthesis of didmolamides A and B, the thiazoline moiety is formed from the trityl protected cysteine 83 by a nucleophilic attack of the cysteine thiol group on the phosphorus-activated amide carbonyl group of the preceding residue (see 84) <05TL2567>. 

The substitution of the hydroxy group by a thiol group (or transformation of the oxo form into the thioxo form) is achieved by treatment with phosphorus pentasulfide (P4S10) in pyridine at reflux temperature. In the case of pyrimido[4,5-c/]pyridazine-2,4-diol (3) it is possible to exchange only the 4-hydroxy group or both hydroxy groups57. 

Kelly s biomimetic methodology, first reported in 2003 (03AG(E)83), has become one of the most reliable routes to thiazolines. In this approach, the phosphorus-activated amide carbonyl group undergoes nucleophilic attack by the cysteine thiol group to provide the thiazoline moiety For example, amide 25 is treated with triphenylphosphine oxide and triflic anhydride to provide thiazoline ester 26 in good yield (13TL3150). 

The Sulphur Cycle.— Unlike phosphorus, sulphur appears in both oxidised and reduced forms in the history of life. Completely oxidised as sulphate, it enters the plant from the soil, and is converted into partially reduced organic compounds containing the thiol group —SH or the disulphide linkage —S—S—. From these, the completely reduced form, HjS, is derived by bacterial degradation either in the soil or in the alimentary tract of the animal. Hydrogen sulphide is attacked by the sulphur-oxidising bacteria, with the ultimate formation of sulphate, which is available for plant absorption. 

Sulfonic acids are prone to reduction with iodine [7553-56-2] in the presence of triphenylphosphine [603-35-0] to produce the corresponding iodides. This type of reduction is also facile with alkyl sulfonates (16). Aromatic sulfonic acids may also be reduced electrochemicaUy to give the parent arene. However, sulfonic acids, when reduced with iodine and phosphorus [7723-14-0]y produce thiols (qv). Amination of sulfonates has also been reported, in which the carbon—sulfur bond is cleaved (17). Ortho-lithiation of sulfonic acid lithium salts has proven to be a useful technique for organic syntheses, but has litde commercial importance. Optically active sulfonates have been used in asymmetric syntheses to selectively O-alkylate alcohols and phenols, typically on a laboratory scale. Aromatic sulfonates are cleaved, ie, desulfonated, by uv radiation to give the parent aromatic compound and a coupling product of the aromatic compound, as shown, where Ar represents an aryl group (18). 

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