Syntheses and Reactions of 2,2-Disubstituted Cyclopentane-1,3-diones, 6. Conversion of 2-Methylcyclopentane-1,3-dione into 5-Methylcycloheptane-1,4-dione via 3-(1-Methyl-2,5-dioxocyclopentyl)propanal

✍ Scribed by Schick, Hans ;Roatsch, Birgit ;Schwarz, Hartmut ;Hauser, André ;Schwarz, Sigfrid

• Publisher: John Wiley and Sons
• Year: 1992
• Tongue: English
• Weight: 453 KB
• Volume: 1992
• Category: Article
• ISSN: 0947-3440
• DOI: 10.1002/jlac.199219920176

✦ Synopsis

Abstract

In contrast to earlier reported unsuccessful experiments the Michael addition of prop‐2‐enal to 2‐methylcyclopentane‐1,3‐dione (1) affords 3‐(1‐methyl‐2,5‐dioxocyclopentyl)propanal (3) in 90% yield, if the reaction is carried out in water without a basic catalyst. This aldehyde is converted by an intramolecular aldol reaction to (±)‐endo‐2‐ and (±)‐exo‐2‐hydroxy‐5‐methylbicyclo[3.2.1]octane‐6,8‐dione (rac‐4 and rac‐6), both affording (±)‐5‐methylcycloheptane‐1,4‐dione (rac‐8) after oxidation to (±)‐5‐methylbicyclo[3.2.1]octane‐2,6,8‐trione (rac‐2), hydrolytic ring‐opening and decarboxylation. This reaction sequence allows the transformation of the 2‐alkylated cyclopentane‐1,3‐dione 1 into the 5‐alkylated cycloheptane‐1,4‐dione rac‐8 in a good overall yield. The pathway of the ringopening process has been determined by an investigation of the reaction intermediates.