Alcohols, acetylenic oxidative coupling

Air, the cheapest oxidant, is used only rarely without irradiation and without catalysts. Examples of oxidations by air alone are the conversion of aldehydes into carboxylic acids (autoxidation) and the oxidation of acyl-oins to a-diketones. Usually, exposure to light, irradiation with ultraviolet light, or catalysts are needed. Under such circumstances, dehydrogenative coupling in benzylic positions takes place at very mild conditions [7]. In the presence of catalysts, terminal acetylenes are coupled to give diacetylenes [2], and anthracene is oxidized to anthraquinone [3]. Alcohols are converted into aldehydes or ketones with limited amounts of air [4, 5, 6, 7], Air oxidizes esters to keto esters [3], thiols to disulfides [9], and sulfoxides to sulfones [10. In the presence of mercuric bromide and under irradiation, methylene groups in allylic and benzylic positions are oxidized to carbonyls [11]. 

A number of syntheses of di- and polyacetylenes has been reported. 1-Iodo-l-alkynes couple with terminal acetylenes under palladium-copper catalysis to give 1,3-diynes thus y-iodopropargyl alcohol and phenylacetylene afford compound 30. Oxidative coupling of 1 -alkynes to yield symmetrical 1,3-diynes is brought about by air and copper(I) chloride in the presence of N, A -tetramethylethylenediamine (equation Trialkylsilyl sub-... 

Standard oxidative coupling methods for acetylenes use the Glaser method (CuCl, NH4CI, aqueous alcohol, O2) or Eglinton and Galbraith s method [Cu(OAc)a, pyridine, alcohol]. The former reaction can be accelerated by addition of JYiV A -tetramethylethylenediamine and the yield improved by using dimethoxyethane as solvent. ... 

Whilst acetylenic alcohols can be employed directly in Cadiot-Chodkiewicz reactions [9], protection of the alcohol (usefully as the Thp ether) is necessary for Castro coupling [14]. A variation based upon these two processes involves coupling of terminal alkynes with 3-bromopropynol (10) in the presence of pyridine [15]. For primary alcohol products, oxidation to the aldehyde with nickel peroxide followed by base-catalyzed decarbonylation generates the new terminal acetylene e.g. Fig. 1.10. 

Takahashi et al. also reported a route to muconin. Their synthesis adopted Keinan et al. s strategy to construct the stereochemistries by Sharpless AD and AE upon multiple olefin containing fatty acid (Scheme 10-35). The di-olefin 214 was subject to Sharpless AD conditions and then treated with acid, yielding a THP-containing diol. This diol was further protected as acetonide 215. The reversion of stereochemistry of alcohol 215 was achieved by Dess-Marlin oxidation and Zn(BH4)2 reduction. Williamson etherification of tosylate 216 and epoxide formation afforded tri-ring intermediate 217. Opening with acetylene, 217 was converted into the terminal alkyne 218, which was coupled with vinyl iodide to finally give muconin. 

Oxidations by oxygen and catalysts are used for the conversion of alkanes into alcohols, ketones, or acids [54]-, for the epoxidation of alkenes [43, for the formation of alkenyl hydroperoxides [22] for the conversion of terminal alkenes into methyl ketones [60, 65] for the coupling of terminal acetylenes [2, 59, 66] for the oxidation of aromatic compounds to quinones [3] or carboxylic acids [65] for the dehydrogenation of alcohols to aldehydes [4, 55, 56] or ketones [56, 57, 62, 70] for the conversion of alcohols [56, 69], aldehydes [5, 6, 63], and ketones [52, 67] into carboxylic acids and for the oxidation of primary amines to nitriles [64], of thiols to disulfides [9] or sulfonic acids [53], of sulfoxides to sulfones [70], and of alkyl dichloroboranes to alkyl hydroperoxides [57]. 

The spectrum of applications of potassium permanganate is very broad. This reagent is used for dehydrogenative coupling [570], hydrox-ylates tertiary carbons to form hydroxy compounds [550,831], hydroxylates double bonds to form vicinal diols [707, 296, 555, 577], oxidizes alkenes to a-diketones [560, 567], cleaves double bonds to form carbonyl compounds [840, 842, 552] or carboxylic acids [765, 841, 843, 845, 852, 869, 872, 873, 874], and converts acetylenes into dicarbonyl compounds [848, 856, 864] or carboxylic acids [843, 864], Aromatic rings are degraded to carboxylic acids [575, 576], and side chains in aromatic compounds are oxidized to ketones [566, 577] or carboxylic acids [503, 878, 879, 880, 881, 882, 555]. Primary alcohols [884] and aldehydes [749, 868, 555] are converted into carboxylic acids, secondary alcohols into ketones [749, 839, 844, 863, 865, 886, 887], ketones into keto acids [555, 559, 590] or acids [559, 597], ethers into esters [555], and amines into amides [854, 555] or imines [557], Aromatic amines are oxidized to nitro compounds [755, 559, 592], aliphatic nitro compounds to ketones [562, 567], sulfides to sulfones [846], selenides to selenones [525], and iodo compounds to iodoso compounds [595]. 

In the area of oxidation catalysis, several interesting reactions have been developed by Waser using a Koser-type hypervalent iodine 71 with an incorporated acetylene ligand (Scheme 16.17). Under catalysis with palladium hexafluoroacetylacetonate, nucleopalladation with both a phenol (e.g., 70) and an acid (e.g., 73) followed by oxidative C(sp )-C(sp) coupling led to new products 72 and 74. Initially, this reaction was developed for cyclization of alcohols or acids, respectively. Both five-and six-membered ring cyclization were successfully employed, and a total of 20 examples with 34-82% yield demonstrate the broad scope of this approach [58]. 

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