Notiz über einen Zugang zu β, γ‐ungesättigten Carbonsäurederivaten mit Hilfe der Amidacetal‐Claisenumlagerung. Über synthetische methoden, 17. Mitteilung

Abstract

Note on a preparation of β, γ‐unsaturated carboxylic acid derivatives using the amide acetal Claisen rearrangement 3‐(Trimethylsilyl)allyl alcohols smoothly undergo the amide acetal Claisen rearrangement furnishing allyl silanes. Subsequent protolysis with HF at −20° provides a convenient, stereoselective method for the preparation of β, γ‐unsaturated carboxylic acid derivatives. Three model examples illustrate the procedure.

Lewis Acid-Catalyzed Regio- and Stereoselective Allylsilation of Simple Unsaturated Hydrocarbons

“…Intermediate III then rearranges to the more stable tertiary carbonium intermediate IV through a 1,5-hydride shift. 22 Finally, 4' can be produced by elimination of the silyl cation.…”

“…The formation of the more stable secondary carbocation and the silyl b-stabilization effect in the intermediate II would be responsible for the regiochemistry of the products. [13][14][15][16][22][23][24] Intermediate II then interacts intramolecularly with the double bond of the other allyl group to form a new carbon-carbon bond to give intermediate III, a cyclic carbenium ion. The b-stabilization effect in intermediate III would be relatively small, since the silyl group is located within the ring frame.…”

[3,3] Sigmatropic Rearrangement of Boron‐Containing Allyl Alcohols: Synthesis of Allyl Addition Reagents

“…Eschenmoser rearrangements7a, 11 gave similar results: At 80 °C allyl alcohol ( E )‐ 5 reacted with the orthoamide to furnish the diastereoisomeric amides 4 b (70 % yield of a 1:1 mixture, separated by medium‐pressure liquid chromatography (MPLC)), while compound 9 gave product 11 b in moderate yield (44 %). No formation of products 4 b was detected when olefin ( Z )‐ 5 was exposed to the same reaction conditions.…”

[3,3]‐Sigmatrope Umlagerungen von Bor‐haltigen Allylalkoholen: Synthese von Allyladditionsreagentien

“…Die Eschenmoser‐Umlagerung7a, 11 lieferte zunächst vergleichbare Resultate: Bei 80 °C reagierte ( E )‐ 5 mit dem Orthoamid, wobei die diastereomeren Amide 4 b erhalten wurden (70 % Ausbeute eines 1:1‐Gemisches, das leicht durch Mitteldruck‐Flüssigkeitschromatographie (MPLC) getrennt wurde); ausgehend von 9 wurde in moderater Ausbeute (44 %) das Umlagerungsprodukt 11 b isoliert. Dagegen wurde bei der Umsetzung von ( Z )‐ 5 nicht das erwartete Produkt 4 b erhalten, sondern das Homoenolat‐Äquivalent 12 als diastereomerenreine, konfigurationsstabile Verbindung.…”