Ketone From thiol

Palladium-mediated syntheses of aldehydes and ketones from thiol esters (many examples of syntheses of A-heterocycles and natural compounds containing heterocyclic fragments) 04ACA87. 

From thiol acids and a-halo ketones Thiols... 

Thioketals, unlike ordinary ketals, are formed readily from ketones and thiols (RSH) in the presence of acid catalysts. The desulfurization procedure usually goes well, but the product is rather difficult to separate by extraction from the large excess of Raney nickel required for optimum yields. 

The reaction of aldehydes or ketones with thiols, usually with a Lewis acid catalyst, leads to dithioacetals or dithioketals. The most common catalyst used is probably boron trifluoride etherate (BF3 OEt2). Similarly reactions that use 1,2-ethanedithiol or 1,3-propanedithiolleadto 1,3-dithiolanes, such as 18 or l,3-dithianes. " Dithioa-cetals can also be prepared from aldehydes or ketones by treatment with thiols in the presence of TiCU, SiCU, LiBp4, AKOTfls, with a disulfide RSSR (R = alkyl or aryl), or with methylthiotrimethylsilane (MeSSiMe3). " ... 

Several reports by Gennari et a/. describe the generation of enolates directly from carbonyl compounds by using ethylenedioxychloroborane (B-chloro-2,5-dioxaborolane 118) in the presence of diiso-propylethylamine. Reactions of these enolates, derived from ketones and thiol esters, with aldehydes provide good yields (60-85%) of aldol adducts, whereas esters give unsatisfactory yields (-30%). V en ethyl ketones or propanethioates are employed, Z )-enolates (119) can be formed exclusively using specific reaction conditions, and excellent syn selectivities (92 8 to 99 1) ate observed (Scheme 48). 

Silyloxy-substituted alkyl radicals, which are generated via addition of tris(trimethylsilyl)silyl radicals to chiral ketones, abstract hydrogen from thiols with moderate diastereoselectivitics37. The svnjunti ratio is dependent on the steric bulk of the neighboring alkyl substituents. 

It should be noted that A-bromo compounds can act as oxidizing agents e.g., A-bromo-acetamide and NBS oxidize secondary alcohols to ketones, and use of this has been made in steroid syntheses.355 Aldehydes, semiacetals, and finally esters are formed from primary alcohols by NBS, and disulfides from thiols (for references see Homer and Winkelmann354). Iodine is liberated from acidified KI solution, a reaction that can be utilized for quantitative determination of NBS and for detection of unchanged NBS in a reaction. 

P-Hydroxy ketones from epoxy ketones. Using thiol/diselenide exchange to generate the benzeneselenolate anion, catalytic reductive ring opening of epoxy ketones is achieved. N-Acetylcycteine may be employed as the supplementary reagent. 

If we want to fix glucose in the open-chain form, we must make an acetal of quite a different kind using a thiol (RSH) instead of an alcohol, an aldehyde, or a ketone. The thiol combines with the aldehyde group of the open-chain form to give a stable dithloacetal. The dithioacetal is evidently more stable than the alternative hemiacetals or monothioacetals that could be formed from the pyranose or furanose forms. 

Note that silyl ketene acetals derived from thiol esters have the opposite Z/E descriptors compared to esters and ketones due to change of sequence rule priority associated with the sulfur atom. 

As described above, two new Cu-catalyzed desulfitative transformations have been discovered that can be used for the construction of peptidyl ketones from peptidic thiol esters and boronic acids. Under aerobic reaction conditions, S -acylthiosalicylamides are effective and efficient, although 2 equiv of the boronic acid are mechanistically required (Scheme 23.6). In comparison, 5 -acyl-2-mercaptoaryloximes function as MT mimics and can produce peptidyl ketones under anaerobic reaction conditions from only a single equivalent of boronic acid. The latter reaction is also efficient and general, but in its current design, it is only catalytically effective at elevated temperatures (>90 C). 

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