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Asymmetric Brønsted Base Catalyzed and Directed [3+2] Cycloaddition of 2-Acyl Cycloheptatrienes with Azomethine Ylides.

Chemistry (Weinheim an der Bergstrasse, Germany) (2016-01-26)
Vibeke H Lauridsen, Lise Ibsen, Jakob Blom, Karl Anker Jørgensen
ABSTRACT

Conjugated cyclic trienes have the potential for different types of cycloaddition reactions. In the present work, we will, in a novel asymmetric cycloaddition reaction, demonstrate that the organocatalytic reaction of 2-acyl cycloheptatrienes with azomethine ylides proceeds as a [3+2] cycloaddition, which is in contrast to the Lewis acid-catalyzed reaction, in which a [3+6] cycloaddition takes place. In the presence of a chiral organosuperbase, 2-acyl cycloheptatrienes react in a highly enantioselective manner in the [3+2] cycloaddition with azomethine ylides, providing the 1,3-dipolar cycloaddition product in high yields and up to 99 % ee. It is also shown that the diene formed by the reaction can undergo stereoselective dihydroxylation, bromination, and cycloaddition reactions. Finally, based on experimental observations, some mechanistic considerations are discussed.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
(S)-2-(2,3-Bis(dicyclohexylamino)cyclopropenimine)-3-phenylpropan-1-ol hydrochloride, ≥95%

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