3-Alkenylation or 3-alkylation of indole with propargylic alcohols could be efficiently controlled by the catalyst. In the presence of triflic acid, 3-alkenylation of indole occurred and a 3,4-dihydrocyclopenta[b]indole skeleton was effectively constructed in moderate to excellent yields via a cascade process. In the presence of Cu(OTf)(2), 3-alkylation of indole resulted in the formation of 3-propargylic indole, which could be further converted into 2-iodo-1,4-dihydrocyclopenta[b]indoles in the presence of N-iodosuccinimide and boron trifluoride etherate. Possible mechanisms related to the 3-alkenylation or 3-alkylation of indole and their extension to the formation of 3,4-dihydrocyclopenta[b]indoles or 1,4-dihydrocyclopenta[b]indoles are postulated and discussed.
Allenephosphoramides were prepared from propargyl alcohols and diethyl arylphosphoramides using Yb(OTf)(3) as catalyst. In the presence of iodine, 4,9-dihydro-2H-benzo[f]isoindole derivatives could be efficiently constructed from the same two starting materials in a single step.
An efficient and straightforward strategy for the synthesis of N-(2-haloinden-1-yl)arenesulfonamides from propargylic alcohols and sulfonamides is described. Allenesulfonamide is postulated to be the key intermediate for this tandem transformation.
We report herein a three-component reaction of propargylic alcohols with 2-butynedioates and secondary amines, which furnished functionalized dihydroazepines. In the cases where benzylmethylamine and benzyl-i-propylamine were used as the secondary amine, the reaction afforded 2,5-dihydro-1H-pyrroles and 2,3-dihydro-1H-pyrroles, respectively, as the major product along with the desired dihydroazepines. The reaction mode depends on the electronic and steric effect of the substitutents on the secondary amines used. A tentative mechanism for this cascade process is postulated. The key intermediate is ascribed to 1,3,4-pentatrien-1-amine, which is formed by trapping the in situ generating allenic carbocation with enamine. Because of the reactivity of 1,3,4-pentatrien-1-amine formed, different products were thus formed.
An efficient and straightforward strategy for the synthesis of 4-methylene-1-(phenylsulfonyl)-4,5-dihydro-1H-pyrazole from propargyl alcohol and N-sulfonylhydrazone is described. N-Sulfonyl allenamide is postulated to be the key intermediate for this tandem transformation.
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