Alkoxy-2-acetylenes

In substrates which do not have this special bias, it may be possible to achieve quite good selectivity in either sense by the appropriate choice of reagent. A particularly useful survey was performed using the acetylenic alkoxy ketone 6-henzyloxy-8-methyl-1-(tctrahydro-2//-pyran-2-yl)oxy-3-nonyn-5-one20. Zinc borohydride again proved the method of choice for the chclation-control unff -produet, while K-Selectride was most effective for the Felkin-Anh yyw-product. 

The direct combination of selenium and acetylene provides the most convenient source of selenophene (76JHC1319). Lesser amounts of many other compounds are formed concurrently and include 2- and 3-alkylselenophenes, benzo[6]selenophene and isomeric selenoloselenophenes (76CS(10)159). The commercial availability of thiophene makes comparable reactions of little interest for the obtention of the parent heterocycle in the laboratory. However, the reaction of substituted acetylenes with morpholinyl disulfide is of some synthetic value. The process, which appears to entail the initial formation of thionitroxyl radicals, converts phenylacetylene into a 3 1 mixture of 2,4- and 2,5-diphenylthiophene, methyl propiolate into dimethyl thiophene-2,5-dicarboxylate, and ethyl phenylpropiolate into diethyl 3,4-diphenylthiophene-2,5-dicarboxylate (Scheme 83a) (77TL3413). Dimethyl thiophene-2,4-dicarboxylate is obtained from methyl propiolate by treatment with dimethyl sulfoxide and thionyl chloride (Scheme 83b) (66CB1558). The rhodium carbonyl catalyzed carbonylation of alkynes in alcohols provides 5-alkoxy-2(5//)-furanones (Scheme 83c) (81CL993). The inclusion of ethylene provides 5-ethyl-2(5//)-furanones instead (82NKK242). The nickel acetate catalyzed addition of r-butyl isocyanide to alkynes provides access to 2-aminopyrroles (Scheme 83d) (70S593). 

An unusual 1,4-migration of a trifluoromethyl group was observed when azomethine imines were synthesized from hexafluoroacetone azine and alkoxy-acetylenes The rearrangement, which occurs at temperatures as low as 0 "C, results in the formation of A-(perfluoro-ferf-butyl)pyrazoles [207] (equation 46)... 

Examples of dehydrobromination leading to bromoethynylpyrazoles as illustrated by Scheme 36 are described in a patent (99USP5925769). Treatment of 1,1-dibromooleflns with tetrabutylammonium fluoride in THE at room temperature for about 24 h under N2 gives the l-bromo-2-(pyrazol-3-yl)acetylenes where R, R, R, and R" are independently selected from H and alkyl, alkoxy. 

Thus, unlike enyne amines, l-alkoxy-l,3-enynes react with 1,3-dipoles by their acetylenic bond. 

A second consequence of the cyclic transition state of these reactions is that (Z)-alkenyl-stannanes are less reactive than their (E)-isomers and can in some cases be recovered unchanged from reactions in which mixtures of isomers are used109. a-Alkoxy-2-butenylstannanes fail to react with 0,/J-dialkylated a./J-unsaturated aldehydes, on heating, and give low syn/anli stereoselectivity with ,/i-acetylenic aldehydes, perhaps because of reduced steric effects110. 

Similarly to aldehydes, esters add to acetylenes to produce unstable oxetenes which decompose to j8-alkoxy-a-benzoylstyrene derivatives when diphenylacetylene is used.<108) For example,... 

As demonstrated in previous sections, the carbazole unit was introduced as a pendant group or as a chain member in major classes of EL polymers such as PPVs (95-105,141,177, 190) and PFs (62, 63, 242-245). A variety of 2,7-carbazole-derived polymers with different conjugated units, such as 2-alkoxy- and 2,5-dialkoxy-l,4-phenylene (549) and l,l -binaphtha-lene-6,6 -diyl (550 [658]), 2,5-pyridine (551), 2,7-fluorene (245 [345,346]), 2,5 -bithiophene (554 [345]), 5,8-quinoxaline (552), quinquethiophene-SjS -dioxide (450 [550]), 2,5-thiophene (553), 2,5-furan (555), and acetylene (556 [659]) were reported by Leclerc and coworkers... 

A number of Mo carbene catalysts, bearing various modified ligands, have been reported and proven to elegantly induce living polymerization of acetylene monomers. The first example is the cyclopolymerization of 1,6-heptadiynes catalyzed by Mo carbenes Mo carbenes ligated by bulky imido and alkoxy groups are quite effective. In... 

Hydrosilylation is formally the addition of the units of R3Si and H (R may be alkyl, alkoxy, or halide) to an unsaturated group such as an olefin, acetylene, or ketone, e.g.,... 

Acetylenic esters react with alkyl azides, aryl azides, carbo-alkoxy azides, and tosyl azide yielding triazoles in all cases studied.102-302-306 When dimethyl acetylenedicarboxylate (92) is the starting material, the 1-substituted 4,5-dicarbomethoxy-1,2,3-triazoles 93 are obtained. 

The relative rates of proton additions to structurally different acetylene and ethylene derivatives shown in Table 8 indicate that the effect of groups, such as phenyl and alkoxy, which can conjugate with the positive charge, is greater for alkenes. Moreover, it is evident from Table... 

Oxidation of acetylenic ethers. 1-Alkoxy-l-alkynes (1) are oxidized by OSO4 (the function of KCIO3 is to regenerate OsO ) to a-keto esters (2) in HjO-ether in 50-80% yield. The paper also reports use of this system for the novel oxidation of 3 to the erythro-isomcT (4) of 3,4-dihydroxyhexane-2,5-dione. ... 

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