Efficient Syntheses of (Thio)phosphonylated Isobenzofurans by Tandem Nucleophilic Addition and Regioselective 5‐exo‐dig Addition to Carbon‐Carbon Triple Bond: Cooperative Effect to 1,8‐Diazabicyclo[5.4.0]undec‐7‐ene (DBU)

Abstract

Abstract:The tandem nucleophilic addition-cyclization reaction of o-alkynylbenzaldehydes or o-alkyn-

Study on the Reactions of Acetylenic Aldehydes with Dimethyl Phosphite in Basic Media: Phosphonate‐Phosphate Rearrangement versus 5‐exo‐dig Cyclization Reactions

“…[4] The triple bonds of o-alkynylbenzaldehydes and o-alkynylacetophenones are electron-rich, so the fact that these materials undergo smooth tandem 5-exo-dig cyclization reaction with dialkyl phosphites in basic media dis-A C H T U N G T R E N N U N G agrees with our observations. So, we synthesized some of o-alkynylbenzaldehydes (2a, c, f) used by the original authors and repeated the optimized reaction of the substrates with dimethyl phosphite (Scheme 5).…”

“…After quick and selective conversions of the starting materials and purification of products 3a, 3'a and 3'e, we performed careful structure elucidations and moreover, we turned our attention to the spectral data of isobenzofuran-1-ylphos-A C H T U N G T R E N N U N G phonates (3) and 1,3-dihydroisobenzofuran-1-ylphos-A C H T U N G T R E N N U N G phonates (3'), published in the original publication. It should be noted that, besides minor discrepancies between chemical shifts, we obtained the same NMR spectra as Miao et al [4] In the 1 H NMR spectra of 3a, 3'a and 3'e, there were doublets for methylene groups at 5.20-5.32 ppm. The coupling constants of 7.1-7.5 Hz pointed to vicinal coupling to neighbouring phosphorus nuclei (Scheme 5).…”

“…All these results showed that the report about tandem nucleophilic addition-cyclization reaction of o-alkynylbenzaldehydes or o-alkynylacetophenones with dialkyl phosphites or dialkyl phosphonothioates in the presence of 1,8- [4] was erroneous.…”

“…[10] However, in the original publication the NMR spectra of 3a, 3'a and 3'e were differently interpreted and other structures for final compounds were proposed (see ref. [4] and the Supporting Information). In order to definitely confirm the structures of compounds 3a, 3'a and 3'e several additional NMR experiments were run.…”

“…[4] According to the procedure in this paper, various isobenzofuran (thio)phosphonate derivatives (3) or (3') were prepared by means of via cooperative DBU intramolecular cyclization of o-alkynylbenzaldehydes or o-alkynylacetophenones (2) and dialkyl phosphite or dialkyl phosphonothioate (1) (Scheme 2).…”