Thiocarbonyl esters

Deoxygenation of primary and secondary alcohols.1 This deoxygenation has been effected by reduction of the thiocarbonyl esters with tributyltin hydride and AIBN as the radial initiator (11, 550). A newer, milder method uses diphenylsilane in a radical chain reaction initiated by triethylborane and air. Even secondary thiono-carbonates, particularly those derived from 4-fluorophenol, are deoxygenated at 25°. 

Deoxygenation of RiCHOH1 (11, 550). Radical deoxygenation of secondary alcohols via thiocarbonyl esters was introduced by Barton and McCombie. More recently, phenoxythiocarbonyl esters have been recommended for the radical deoxygenation (10, 306-307). Particularly rapid and quantitative reduction can be obtained using 2,4,6-trichlorophenoxy- or pentafluorophenoxythiocarbonyl esters. 

Foster and Wolfrom, in 1956, encountered an anomalous reaction of methyl 3,4-0-isopropylidene-2-0-(sodium thiolthiocarbonyl)- S-D-arabino-pyranoside (LIX) with certain alkyl halides, namely ethyl iodide, propyl bromide, isopropyl bromide, and ter<-butyl chloride. The expected 2-0-[(alkylthio)thiocarbonyl] esters LX were not formed, but, in each case, bis(methyl 3,4-0-isopropylidene-j8-D-arabinopyranoside) 2-thionocarbonate (VI) was isolated. A probable explanation of this behavior was suggested... 

PTOC (pyridine thiocarbonyl) esters as the radical precursors and competing trapping agents (Scheme 15.4S) [122c]. 

The introduction of 0-acyl thiohydroxamates (mixed anhydrides of carboxylic acids with thiohydroxamic acids) by the Barton group in 1983 [1] has provided one of the mildest and most convenient and versatile sources of carbon-centered radicals which fulfill the above criteria, and can hence, in Sir Derek s own words, be described as disciplined . Since their preparation from carboxylic acids is extremely straightforward, and since they have demonstrated a rapacious radicophilicity in a wide variety of very useful transformations, it is no surprise that these derivatives are commonly named either as Barton esters or by the acronym PTOC (pyridine thiocarbonyl) esters. The ongoing development of this chemistry has been summarized over the years in several useful reviews [2], and some of the tried and tested experimental procedures have also been collated [3]. 

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