The first asymmetric Carroll rearrangement opens up an efficient access to highly functionalised ketones 4 and 7 with vicinal quaternary and tertiary stereogenic centres of excellent diastereo-and enantiomeric purity (de = 89-96%, ee = 82 to >98%) by using the SAMP/RAMP hydrazone methodology. Starting from hydrazones (S)-2, we describe a dianionic and a Lewis acid-mediated variant of the [3.3]-sigmatropic Carroll rearrangement. The relative and absolute configuration of the new stereogenic centres created by C-C bond formation were assigned by X-ray crystallographic analysis of the hydrazones 3h and 3j.The diastereo-and enantioselective generation of compounds bearing quaternary stereogenic centres as building blocks in natural product and drug synthesis is an attractive field in synthetic organic chemistry. In recent years many reports have been published concerning the creation of quaternary stereogenic centres" p71, although only a few allow the simultaneous preparation of adjacent stereogenic centresLsI. Intramolecular transformations such as sigmatropic rearrangements are highly suitable for this purpose, as for example the Ireland rearrangement, an important variation of the Claisen rearrangementL91. Due to the concerted, suprafacial nature of the Claisen rearrangement and the strong conformational preference for highly ordered chair-like transition states, in general products with high enantiomeric excesses are obtained. Asymmetric Ireland rearrangements with moderate to excellent asymmetric inductions have been described [lO]. The Carroll rearrangement ["] is such a tool, too. Although known since 1940, only a few diastereoselective[l2l or chirality transfer rearrangements ["] leading to optically active rearrangement products, have been described. Many different variations of the Carroll rearrangement are known, most of which proceed with decarboxylation of the initially formed p-ketoThe Carroll rearrangement has received much attention in the last few years due to the discovery of the dianionic variant[l5I. Recently, we have reported on the first asymmetric dianionic Carroll rearrangement and demonstrated in a short communication an efficient diastereo-and enantioselective synthesis of highly functionalised ketones [16]. In this paper we describe the asymmetric dianionic Carroll rearrangement in full detail and in addition a Lewis acid-mediated variant of the Carroll rearrangement. As depicted in Scheme 1, both types of rearrangements of hydrazono esters A lead to the highly functionalised products D although different diastereomers were obtained, due to the different transition states. While in the dianionic pathway dilithium or dialiminium P-hydrazono ester dienolates B undergo the rearrangement, in the Lewis acid-mediated pathway the ketene acetal C reacts.
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