N-Hydroxy-2-thiopyridone

Fundamentally, O-esters of N-hydroxy-2-thiopyridone are photo-lyzed in the presence of an excess of white phosphorus in a methylene chloride/carbon disulfide medium. On solvent removal, hydrolysis, and oxidation with hydrogen peroxide, good yields of phosphonic acids (Figure 2.10) bearing the carbon functionality of the parent acid are isolated. 

Scheme 5-5. Reagents and conditions a NaOCE Ph, THF/DMF 5 1, — 10°C to room temperature, b LiAlELt, Et20, reflux, c AC2O, Py. d (1) Cat. RuCh/NaKTt, CCI4/ MeCN/H20 1 1 1.5, room temperature. (2) LiOH, THF/H20 5 4, 0°C. (3) 2N HC1, Et20, 0°C to room temperature, e (1) IV-methylmorpholine, isobutylchloroformate, N-hydroxy-2-thiopyridone, THF, NEt3, TFIF, — 15°C, (2) t-butyl mercaptan, irradiation, THF, room temperature, f H2, 10% Pd/C, EtOFI. g Cat. ( -Pr)4NRu04, NMO, 4 A MS, CH2CI2, room temperature.

A solution of sulfur (S8, 74 mg, 0.29 mmol) and adamantanecarboxylate ester of N-hydroxy-2-thiopyridone (290 mg, 1 mmol) in dichloromethane (15 ml) was irradiated with a tungsten lamp for 1 h under a nitrogen atmosphere at 0 °C. After the reaction, a solution of NaBH4 (20 mmol) in methanol (10 ml) was added drop wise over 15 min to the reaction mixture at room temperature, and the mixture was stirred for one hour. After the reaction, 1 M sulfuric acid (60 ml) was added to the mixture, and then the solution was extracted with dichloromethane (4 X 20 ml), and dried over Na2S04. After removal of the solvent, the residue was purified by column chromatography on silica gel (eluent hexane/ethyl acetate = 97/3) to provide adamantanethiol in 88% yield [33]. 

The photolysis of Barton esters (N-hydroxy-2-thiopyridone esters, 43) proved to be an efficient method for generating carbon-centered radicals that are exploited for the regioselective alkylation of electron-deficient olefins a thiopyridyl unit is likewise incorporated into the end products. In a recent application, Barton esters were found useful in the synthesis of natural and unnatural disubstituted maleimides or maleic anhydrides by way of two consecutive radical addition steps, as described in Scheme 3.27 [72]. 

N-Hydroxy-2-thiopyridone, radical reactions of 89PS(43)349 90-YGK641. 

Barton, D. H. R., Jaszberenyi, J. C., Morrell, A. I. The generation and reactivity of oxygen centered radicals from the photolysis of derivatives of N-hydroxy-2-thiopyridone. Tetrahedron Lett. 1991,32, 311-314. 

The generation and synthetic use of carbon radicals obtained by light-initiated elimination of carbon dioxide from thiohydroxamic esters and in particular from esters of N-hydroxy-2-thiopyridone have again been widely reported. The mechanism... 

The radical EtOCOCMe2COO, generated by photolysis of the corresponding Barton (N-hydroxy-2-thiopyridone) ester, decarboxylates inefficiently unless generated in benzene under reflux. Under these conditions 2-pyridyl-SCMe2-C02Et is obtained in 80% yield. Investigation of the reaction of the decarboxy-... 

RCOOH - RHNi. Acyl derivatives (2) of N-hydroxy-2-thiopyridone (12,417 14,268) when photolyzed in the presence of this diazirine (1) transfer the alkyl group to 1 to form the imine 3. These imines are hydrolyzed by boric acid in refluxing ethanol to primary amines (4). 

D-glucosamine, Tetrahedron Asymm., 5, 2137, 1994 (s) Barton, D. H. R., Chern, C.-Y., and Jas-zberenyi, J. Cs., Homologation of carboxylic acids by improved methods based on radical chain chemistry of acyl derivatives of N-hydroxy-2-thiopyridone, Tetrahedron Lett., 33, 5013, 1992 (t) Barton, D. H. R., Chem, C.-Y., and Jaszberenyi, J. Cs., Two carbon homologation of carboxylic acids via carbon radicals generated from the acyl derivatives of N-hydroxy-2-thiopyridone synthesis of n-l-2 a-keto-acids from Q, acids. (The three carbon problem). Tetrahedron Lett., 33, 5017, 1992. 

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