13C NMR of pterocarpans

Chalmers, Anthony A.; Rall, Gerhardus J. H.; Oberholzer, Maria E.

doi:10.1016/0040-4020(77)84051-9

Cited by 33 publications

(20 citation statements)

References 10 publications

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“…The former value is in excellent agreement with the shift of 31.5-32.5 pprn reported for the natural pterocarpans 6 (27,28) Thus the structures of the isomeric rearrangement products isolated in our laboratory are firmly supported by their nmr spectra. Their mass spectra feature prominent molecular ion and methyl cleavage (M -15) peaks but n o significant differences in the fragmentation patterns that would allow a distinction between the different heterocyclic ring systems.…”

Section: Discussionsupporting

confidence: 79%

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The Claisen rearrangement of 1,4-bis(m-methoxyphenoxy-)2-butyne

Kiehlmann¹,

Li²,

Millar³

1986

Can. J. Chem.

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. Can. J. Chem. 64, 1989Chem. 64, (1986. The Claisen rearrangement of 1,4-bis(m-methoxyphenoxy-)2-butyne (lb) gives four isomeric dimethoxy-6H-benzofuro[3,2-c]-6a, 1 la-dihydro-1 la-methylbenzopyrans (3), three dimethoxy-4b,9b-dihydro-4b,9b-dimethylbenzofuro[3 2 b]benzofurans (4), and, in the presence of acid, three dimethoxy-5a,l0b-dihydro-5a,l0b-dimethylbenzofuro[2,3-b]benzofurans (5), which have been separated and identified by proton and 13C nrnr spectroscopy. Based on the isolation of two chromene intermediates and their conversion to 3 and 4, as well as the isomerization of 3 to 4 and 4 to 5, a "double Claisen" mechanism is proposed. The reaction is not regiospecific but the two [3,3] sigmatropic shifts occur preferentially to the para positions of the methoxy substituents.E. KIEHLMANN, E. P.-M. LI et J. G. MILLAR. Can. J . Chem. 64, 1989Chem. 64, (1986. La transposition de Claisen appliquCe au bis(m-mCthophCnoxy)-1,4 butyne-2 ( l b ) conduit a quatre dilnCthoxy 6H-benzofuro[3,2-cl dihydro-6a,lla mCthyl-lla benzopyrannes isomeres (3), 2 trois dimCthoxy dihydro-4b,9b dimCthyl-4b,9b benzofurol3,2-b] benzofurannes (4) et, en prCsence d'acides, a trois dimCthoxy dihydro-5a,lOb dimCthy1-5a,lOb benzofuro[2,3-b] benzofurannes (5) qui ont CtC sCparCs et identifiks par spectroscopie rmn 'H et 13C. En se basant sur le fait que l'on a is016 deux chromenes intermkdiaires, que ceux-ci ont pu &re transformks en 3 et 4 et que l'on a pu realiser les isomCrisations 3 + 4 et 4 -+ 5, on propose un mCcanisme impliquant un ((double Claisen.. La rCaction n'est pas rCgiospCcifique; toutefois les deux dCplacements sigmatropiques [3,3] se produisent prCf6rentiellement vers les positions para des substituants mithoxy.[Traduit par la revue]

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Section: Discussionsupporting

confidence: 79%

“…The 13C chemical shifts of 11 compounds prepared in our laboratory and 8 closely related compounds reported in the literature (8,10,12,27,28) are listed in Table 3.…”

Section: Discussionmentioning

confidence: 99%

The Claisen rearrangement of 1,4-bis(m-methoxyphenoxy-)2-butyne

Kiehlmann¹,

Li²,

Millar³

1986

Can. J. Chem.

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“…spectra of pterocarpans (6 values hQuartet, acid in chloroform gave neopranol (24) (6 4.61, t, H-2'; 3.08, d, J 10 Hz, H-3') while treatment with m-chloroperbenzoic acid containing a trace of toluene-fi-sulphonic acid lo gave neorautanol (7) in good yield (6 3.74, t, J 5.6, H-3'; 3.06, q, J 16 and 5.6, H-4'a; 2.72, q, J 16 and 5. 6 Hz, H-4'b). Acid-catalysed dehydration of (7) also completes the total synthesis of neorautenane (1).…”

Section: The Use Of Neorautanenia Species In Central and Southernmentioning

confidence: 97%

“…Hydrolysis and intramolecular cyclization in an acid medium gave moderate conversion into 2,3dihydro-7-hydroxy-4H-l-benzopyran-4-one (1 6). Protect ion of the 7-hydroxy-f unction through benzylation, followed by sodium borohydride reduction, afforded 7-benzyloxy-2,3-dihydro-4H-l-benzopyran-4-ol (18) spectrum showed two high-field 3 H-singlets at 6 1.39 and 1.42 assigned to the gem-dimethyl group adjacent to an oxygen function while the protons of the aromatic methoxy-groups absorbed at 6 3.72 (3 H) and 3.94 (3 H). The rest of the spectrum (Table) is consistent with the proposed structure.…”

Section: The Use Of Neorautanenia Species In Central and Southernmentioning

confidence: 99%