The addition of lithiatedalkoxyallenes to N‐tosylimines followed by base‐, silver‐, or gold‐promoted cyclization of the addition products efficiently provides 2,5‐dihydropyrroles, which are excellent substrates for further transformations. Acids promote the hydrolysis of the enol ether moiety to deliver pyrrolidin‐3‐ones, and bases promote the aromatization to the elusive 3‐alkoxypyrroles.
3-Hydroxypyrroles and 1H-pyrrol-3(2H)-ones. Part 13. Reactions of methoxymethylene Meldrum's acid with 3-hydroxypyrroles, with 3-methoxypyrroles and with other active substrates, and pyrolytic heterocyclisations of the products
作者:Paul A. Derbyshire、Gordon A. Hunter、Hamish McNab、Lilian C. Monahan
DOI:10.1039/p19930002017
日期:——
Methoxymethylene Meldrum's acid 2 in acetonitrile solution acts as a useful C-electrophile for active substrates such as pyrrole, indole or tertiary enaminones to give substitution products (e.g. 5, 6 or 12, respectively). Primary enaminones react exclusively at the nitrogen atom under these conditions. The effect of ring substituents on the regiochemistry of electrophilic substitution of 3-hydroxypyrroles and 3-methoxypyrroles was studied using methoxymethylene Meldrum's acid as the electrophile. Flash vacuum pyrolysis of the Meldrum's acid derivatives obtained in many of these reactions gave access to a range of heterocyclic systems, including the pyridone 48, quinolinedione 43, benzazepinedione 41 and fused pyrones 50, 52 and 54.