Rearrangement of optically active ethyl (E)-3-methyl-3-phenylglycidate. Evidence for concerted carbethoxy migration

Aromatization of arene 1,2-oxides. 1-Carboxy- and 1-carboalkoxybenzene oxides

“…As expected, methyl substitution at the 2 or 4 position of 13 increases the rate of oxirane ring opening and favors formation of cation 21 to the total exclusion of oxirane ring opening in the other direction to afford a methyl-substituted salicylic acid. The greater stability of 19 (relative to 20) may be a result of a decrease in the proportion of arene oxide tautomer in 19 and supports the con-clusion3 that methyl substitution on the oxirane ring leads to enhanced stability over methyl substitution at another position.…”

“…Preparation and Aromatization of 19 and 20. When ester 4d was hydrolyzed under identical experimental and workup conditions for the preparation of 13, evaporation of the ether afforded a yellow, crystalline solid that was shown by NMR analysis to be a mixture of 19 and o-cresol (30:70). Neat arene oxide 19 was extremely unstable at room temperature, and purification attempts under optimal conditions gave only the same mixture with an enrichment of 19 Attempts to prepare 20 from 4e by the above method yielded only p-cresol.…”

Unusual 1,2‐Acyl Rearrangement Accompanying Ring Expansion Reaction of Alkaloid Cotarnine under the Action of α‐Haloketones: a New Route to 5‐Acyl‐1,2‐dihydro‐3‐benzazepine Moiety

“…The second possible mechanism is based on competitive Darzens reaction of the substrate tautomer 1B and subsequent carbocation mediated rearrangement of the formed acyl oxiranes 11 (Scheme ). It is well known that acyl oxiranes are prone to 1,2‐AR by carbocationic mechanism . In our case, the AR of oxiranes the 11 should involve the formation of the open‐chain carbocations 12 and their isomerization (also via 1,2‐acyl migration) into carbocations 13 .…”

Gold‐Catalyzed Oxidative Rearrangement Involving 1,2‐Acyl Migration: Efficient Synthesis of Functionalized Dihydro‐γ‐Carbolines from α‐(2‐Indolyl) Propargylic Alcohols and Imines

“…Intermediate 12 might also be stabilized by the nitrogen atom adjacent to the gold carbenoid. Lewis acid catalyzed 1,2carbonyl migrations in pinacol-type rearrangements have been observed for chlorohydrins, [17] a,b-epoxyketones, [18] and esters; [19] for these processes, a concerted mechanism involving neighboring-group participation by the carbonyl group was suggested. [18d] In summary, we have developed a gold-catalyzed synthesis of highly functionalized dihydro-g-carbolines by the cyclization of a-(2-indolyl) propargylic alcohols with imines in the presence of 8-isopropylquinoline N-oxide as the oxidant.…”