1,2-Amino Alcohols and Their Heterocyclic Derivatives as Chiral Auxiliaries in Asymmetric Synthesis

Stereoselective Aldol Condensations

Gingerols and shogaols: Important nutraceutical principles from ginger

Strategy and methodology development for the total synthesis of polyether ionophore antibiotics.

Acceptor-substituted lithio compounds LiACR1R2, in which the acceptor A is an RC(0), NC, RSO2, RS(O)NR, RSO, RS, O2N, or RC(NNR2) group, have long played an important role in organic synthesis. Their significance has grown still further in the last fifteen years, as one has increasingly learnt to employ them successfully in chemo-, regio-, diastereo-and enantioselective reactions. Remarkably, little if anything was known of the structures of these compounds. It is therefore not surprising that interest in the structures of this class of compounds has greatly increased in recent years. In the following review, we shall summarize recent research into the structures of the lithio compounds of sulfones, sulfoximides, sulfoxides, thioethers and 1,3-dithianes, nitriles, nitro compounds, and hydrazones. Crystal structure determinations from recent years are central to this study. They are supplemented by solution studies and by calculations of structures. Structural similarities and differences between the individual states of aggregation are pointed out wherever possible, as is also the relationship between structure and reactivity.

The Structure of Lithium Compounds of Sulfones, Sulfoximides, Sulfoxides, Thioethers and 1,3-Dithianes, Nitriles, Nitro Compounds and Hydrazones

Aldehyde und cyclische Ketone werden mit (S)-1-Amino-2-(methoxymethyl)pyrrolidin (13) (SAMP) in die entsprechenden chiralen SAMP-Hydrazone 1 ubergefuhrt, die mit Lithiumdiisopropylamid in Tetrahydrofuran in α-Stellung metalliert werden konnen. Die resultierenden chiralen “Azaenolate” 2 werden bei —95°C zu Produkthydrazonen 3 alkyliert, die durch Ozonolyse bzw. Hydrolyse uber Methoiodide 15 zu optisch aktiven, α-chiralen Carbonylverbindungen 5 gespalten werden. Die Methode gestattet die enantioselektive Alkylierung von Aldehyden und cyclischen Ketonen in chemischen Gesamtausbeuten von 51–80% und in hoher bis zu volliger Enantioselektivitat. Die chirale Hilfsverbindung “SAMP” wird unter Verwendung des “chiralen pools” in 4 Stufen aus (S)-Prolin (12) uber 9,10 und 11 bzw. in 6 Stufen uber 9,6,7,8 und 11 hergestellt. Es wird gezeigt, das α-chirale Aldehyde mit dem BH3 THF-Komplex racemisierungsfrei zu β-chiralen Alkoholen 16 reduziert werden konnen. Eine “synthon-kontrollierte Enantioselektivitat” wird am Beispiel der enantioselektiven Synthese von (R)- und (S)-2-Methylbutanal (51, 51′) demonstriert.



Asymmetric Synthesis via Metalated Chiral Hydrazones. Enantioselective Alkylation of Cyclic Ketones and Aldehydes



Aldehydes and cyclic ketones are converted with (S)-1-amino-2-(methoxymethyl)pyrrolidine(13) (SAMP) to the corresponding chiral SAMP-hydrazones 1, which can be metalated in α-position by lithium diisopropylamide in tetrahydrofuran. The resulting chiral “azaenolates” 2 are alkylated at — 95°C to product hydrazones 3, which are cleaved to optically active α-chiral carbonyl compounds 5 by ozonolysis or hydrolysis via methoiodides 15. The method allows the enantioselective alkylation of aldehydes and cyclic ketones in overall chemical yields of 51–80% and in high, up to complete enantioselectivity. The chiral auxiliary “SAMP” is prepared using the “chiral pool” in 4 steps from (S)-proline (12) via9, 10 and 11 or in 6 steps via9, 6, 7, 8 and 11. It is shown that α-chiral aldehydes can be reduced with BH3 THF-complex to β-chiral alcohols 16 without racemization. A “synthon-controlled enantioselectivity” is demonstrated in the case of the enantioselective synthesis of (R)- and (S)-2-methylbutanal (51, 51′).

Asymmetrische Synthesen via metallierte chirale Hydrazone. Enantioselektive Alkylierung von cyclischen Ketonen und Aldehyden1

Asymmetric Synthesis of α-Substituted Ketones by Metalation and Alkylation of Chiral Hydrazones†

Enantioselective alkylation of aldehydes via metalated chiral hydrazones

Asymmetrische Synthese von α‐substituierten Ketonen durch Metallierung und Alkylierung chiraler Hydrazone

Stereoselective formation and electrophilic substitution of aldehyde hydrazone lithio anions

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