A New Synthesis of Indigo

✍ Scribed by Prof. Dr. E. Ziegler; Dr. Th. Kappe

• Publisher: John Wiley and Sons
• Year: 1964
• Tongue: English
• Weight: 129 KB
• Volume: 3
• Category: Article
• ISSN: 0044-8249
• DOI: 10.1002/anie.196407542

✦ Synopsis

compound; however, Karplus' rule [5] does not strictly apply to four-membered rings. In boiling xylene, both (3) and (4) are converted almost quantitatively into the same acyclic acylpropenyl propyl ether (5). The structure of (5) was determined from elemental analysis, N M R and infrared spectra, and from acid hydrolysis to form l,l-diphenylbutan-2-one.

Dimethylketene also adds onto both trans-and cis-propenyl propyl ether stereospecifically to yield diastereoisomeric cyclobutanones. Again the cis-form reacts faster. In the N M R spectra, the doublet for the tertiary proton on C-3 appears at 6.52 T (Jac = 6.4 cps) in the trans-adduct and at 6.12 T (Jac = 8.3 cps) in the cis-adduct. The stereoselective cis-addition renders the formation of a n intermediate such as (2) improbable. We assume that a onestage multicentered cycloaddition takes place.