Features of the base-catalyzed reaction of 1-vinyl-4,5-dihydro-1H-benzo[g]indole-2-carbaldehyde with phenylacetylene

2-(1-Hydroxypropyn-2-yl)-1-vinylpyrroles: the first successful Favorsky ethynylation of pyrrolecarbaldehydes

“…After comparative analysis of the available literature data [21–23] and consequent optimization of the reaction conditions we have found that the superbasic catalytic composition NaOH/EtOH/DMSO (the molar ratio 1:1.6:13.6) and a temperature of 7–10 °C (Table 1), which is by ca. ten degrees higher than recommended in the patent [22], are appropriate for the efficient ethynylation of 1-vinylpyrrole-2-carbaldehydes with acetylene.…”

“…ten degrees higher than recommended in the patent [22], are appropriate for the efficient ethynylation of 1-vinylpyrrole-2-carbaldehydes with acetylene. As alkali metal hydroxide for the superbase composition we have chosen NaOH since the more basic KOH was shown to promote a subsequent chalcone formation after ethynylation of 4,5-dihydrobenzo[ g ]indole-2-carbaldehyde (which contains a pyrrole-2-carbaldehyde moiety) with phenylacetylene [21]. As shown on the example of benzaldehyde [22], other ratios of the catalytic composition give inferior yields of the corresponding acetylenic alcohol.…”

“…As to the substituents effect on the reaction studied, the variation of yields (mainly 53–68%) is not wide enough to make a reliable conclusion, although the higher yield of acetylenic alcohol 2d (94%) corresponds to the expectation of the enhanced electron-withdrawing effect of the 3-metoxyphenyl group compared to the unsubstituted phenyl ( 1c → 2c ) that should increase the electrophilicity of the carbonyl function. The range of isolated yields is attributable not only to the difference in the reactivity of aldehydes 1a–j , but also to the propensity of the product to undergo acetylene–allene isomerization to give the polymerizable vinyl ketones [21]. As seen from Table 1, the reaction tolerates a wide scope of pyrrole-2-carbaldehydes including those possessing aromatic and heteroaromatic substitution at the 5-position, fused aliphatic and aromatic ring systems, and even the 4,5-unsubstituted parent compound 1a .…”

Transition-Metal-Free Catalytic Formal Hydroacylation of Terminal Alkynes

“…However, these A 3 -coupling systems require the use of transition-metal catalysts and (super)­stoichiometric amounts of amines. Interestingly, when the Favorskii reaction, i.e., the addition of terminal alkynes to carbonyl compounds to afford propargylic alcohols using strong bases, e.g., KOH, , t BuOK, , and Bu 4 NOH, is performed using an aromatic aldehyde as the substrate, the side reaction to produce an α,β-unsaturated carbonyl compound occurs . This side reaction can be regarded as a transition-metal-free formal hydroacylation; however, these systems require strong basic conditions, and the substrate scopes are quite limited.…”