Claisen rearrangement of some (substituted allyl)indoles

Abstract

l-Phenyl-2-arylcyclopropanols. These compounds were prepared from the corresponding acetates by reaction with methyllithium and work-up in boric acid solution as previously described.16 The alcohols are air and base sensitive, and must be stored in polyethylene bottles in the freezer. Their melting points tended to vary depending upon their method of recrystallization, and were broad in range.cis-l,2-Diphenycyclopropanol had mp 79-82.5°( hexaneether), nmr (CDCI3) 1.65 (m, 2 ), 2.21 (s, 1 H, OH), 2.49 (dd, 1 H), 7.33 (d, 10 H). trans-l-2-Diphenylcyclopropanol had mp 96.5-99°(hexaneether), nmr (CDCI3) 1.65 (m, 2 H), 2.53 (s, 1 H), 2.77 (dd, 1 H), 7.03, 7.18 (m, 10H).trans-l-Phenyl-2-(4-methylphenyl)cyclopropanol had mp 75-77°.Kinetic Procedures. Kinetics were run in 60:40 v/v dioxanewater with either perchloric acid or sulfuric acid as catalyst, or in 95% ethanol with NaOH as catalyst. For the acid-catalyzed reactions an appropriate amount of the alcohol or acetate (0.01-0.03 g) was accurately weighted into a 100-ml volumetric flask and the flask was allowed to equilibrate with the constant-temperature bath for 2 min. The flask was then filled to the mark with the acid solution, which was already at thermal equilibrium with the bath.

Biosynthesis of aromatic isoprenoids. Part 5. The preparation of 1-(3,3-dimethylallyl)-L-tryptophan and cyclo-L-aianyl-1-(3,3-dimethylallyl)-L-tryptophan and their non-incorporation into echinulin

“…In particular N-crotylindole (8a) formed the 3-( 1-methylallyl) derivative (8b) at elevated temperatures, presumably via the product (9a) of aza-Claisen rearrangement . 20 However, other model N-allylindole derivatives were thermally stable 21 and the reverse rearrangement (9b)+(8c) has been observed indirectly.22 On the other hand, Casnati and Pochini have reported the facile rearrangement of the (dimet h ylallyl) indole (8c) to the 2-subst it ut ed-indoles (8d) and (8e) in trifluoroacetic acid.23 The ' reversed ' prenyl substituent in (8d) is believed to arise via acidcatalysed aza-Claisen rearrangement to (9b), followed by acid-catalysed 1,2-migration of the prenyl On the basis of these considerations, we decided to synthesise 1-(dimethylally1)-L-tryptophan (2b) and the derived diketo-piperazine (4a) and test their efficiencies as biosynthetic precursors of echinulin.…”

Brønsted Acid Catalyzed Enantioselective Indole Aza-Claisen Rearrangement Mediated by an Arene CH–O Interaction

“…We were drawn to the aromatic aza-Claisen rearrangement because of its potential for generating medicinally valuable aromatic amines . Given the prevalence of indoles in biologically active molecules, we were interested in developing an enantioselective [3,3]-rearrangement around the indole scaffold (Scheme b). − , The discovery of a catalytic enantioselective variant of this reaction could provide a novel approach to chiral 2-subsitituted indoles …”