Epoxide-alkyne reaction

Bis(trifluoromethyl) peroxycarbonate, 705 Bis(trifluoromethyl) peroxydicarbonate, 705 Bis(trifluoromethyl) trioxide IR spectrum, 740 O NMR spectroscopy, 182 Bis(trifluoromethyl) tiioxydicarbonate, 740 Bis(trimethylsilyl) monoperoxysulfate Baeyer-Vilhger oxidation, 785 catalytic epoxidation, 791-2 Bis(trimethylsilyl) peroxide (BTSP) alcohol oxidation, 787-90 alkyne reactions, 800 aromatic compounds, 794-5 Baeyer-Vilhger ketone oxidation, 784-7 demethylation, 798... 

The use of these materials in a range of reactions [isomerization of alkenes and alkynes, C—C bond formation, aldol condensation, Knoevenagel condensation, nitroaldol reactions, Michael addition, conjugate addition of alcohols, nucleophilic addition of phenylacetylene, nucleophilic ring opening of epoxides, oxidation reactions, Si—C bond formation, Pudovik reaction (P—C bond formation) and synthesis ofheterocycles] have been discussed in detail by Ono [248], as well as in the other cited reviews. We will thus discuss here only selected examples. 

Reactions with Epoxides. These reactions allow preparation of /3-alkynic alcohols (eq 4) the use of -butyllithium, followed by diethylaluminum chloride, may increase the yield. 

In the presence of catalytic amount of Cu(NCMe)4NTf2 (4 mol %), 4-methoxypyridine A -oxide (2 equiv) promotes the oxidative cyclization of alkynyl oxiranes and oxetanes (eqs 15 and 16). The mild reaction conditions tolerate a breath of functional groups such as distal epoxides, alkynes, ethers, acetamide, tosylamide, and aryl halides. 

The synthesis of p-hydroxy triazoles by the three-component reaction of a variety of epoxides, sodium azide, and diverse terminal alkyne reactions performed... 

General Reaction Chemistry of Sulfonic Acids. Sulfonic acids may be used to produce sulfonic acid esters, which are derived from epoxides, olefins, alkynes, aHenes, and ketenes, as shown in Figure 1 (10). Sulfonic acids may be converted to sulfonamides via reaction with an amine in the presence of phosphoms oxychloride [10025-87-3] POCl (H)- Because sulfonic acids are generally not converted directiy to sulfonamides, the reaction most likely involves a sulfonyl chloride intermediate. Phosphoms pentachlotide [10026-13-8] and phosphoms pentabromide [7789-69-7] can be used to convert sulfonic acids to the corresponding sulfonyl haUdes (12,13). The conversion may also be accompHshed by continuous electrolysis of thiols or disulfides in the presence of aqueous HCl [7647-01-0] (14) or by direct sulfonation with chlorosulfuric acid. Sulfonyl fluorides are typically prepared by direct sulfonation with fluorosulfutic acid [7789-21-17, or by reaction of the sulfonic acid or sulfonate with fluorosulfutic acid. Halogenation of sulfonic acids, which avoids production of a sulfonyl haUde, can be achieved under oxidative halogenation conditions (15). 

The molybdenum-catalyzed oxidation of alkynes by /-butyl hydroperoxide has been investigated 73JCS(P1)2851) (the epoxidation of alkenes by this system has become an important reaction Section 5.05.4.2.2(i)) but the formation of oxirenes was excluded. 

Heteropoly acids can be synergistically combined with phase-transfer catalysis in the so-called Ishii-Venturello chemistry for oxidation reactions such as oxidation of alcohols, allyl alcohols, alkenes, alkynes, P-unsaturated acids, vic-diols, phenol, and amines with hydrogen peroxide (Mizuno et al., 1994). Recent examples include the epoxidations of alkyl undecylenates (Yadav and Satoskar, 1997) and. styrene (Yadav and Pujari, 2000). 

Scheme 4.10 gives some examples of application of alkyne carboalumination in synthesis. The reaction in Entry 1 was carried out as part of a synthesis of the immunosuppressant drug FK-506. The vinyl alane was subsequently transmetallated to a cuprate reagent (see Chapter 8). In Entry 2, the vinyl alane was used as a nucleophile for opening an epoxide ring and extending the carbon chain by two atoms. In Entries 3 to 5, the vinyl alane adducts were converted to vinyl iodides. In Entry 6, the vinyl alane was converted to an ate reagent prior to reaction with formaldehyde. 

By combining several click reactions, click chemistry allows for the rapid synthesis of useful new compounds of high complexity and combinatorial libraries. The 2-type reaction of the azide ion with a variety of epoxides to give azido alcohols has been exploited extensively in click chemistry. First of all, azido alcohols can be converted into amino alcohols upon reduction.70 On the other hand, aliphatic azides are quite stable toward a number of other standard organic synthesis conditions (orthogonality), but readily undergo 1,3-dipolar cycloaddition with alkynes. An example of the sequential reactions of... 

If epoxidation is accepted as [2 + l]-cydoaddition, then the rare transformation of an allenyl ketone to an isolable allene oxide should be mentioned [170]. The Pau-son-Khand reaction, probably the best known of the [2 + 2 + l]-cycloadditions, can also be performed using an alkyne and an allene, the latter replacing a simple alkene. These reactions were summerized recently by Brummond also induding acceptor-substituted allenes [361]. 

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