ChemInform Abstract: ASYMMETRIC SYNTHESES VIA METALATED CHIRAL HYDRAZONES. OVERALL ENANTIOSELECTIVE α‐ALKYLATION OF ACYCLIC KETONES

Abstract

Die durch Reaktion des Pyrrolidins (I) mit den Ketonen (II) entstandenen Hydrazone (III) reagieren mit den Halogeniden (IV) weiter zu den Hydrazonen (V).

Formation, Alkylation, and Hydrolysis of Chiral Nonracemic N-Amino Cyclic Carbamate Hydrazones: An Approach to the Enantioselective α-Alkylation of Ketones

“…Flash chromatography over silica gel using 5:95 Et 2 O/pentane gave ( R ) - 36 as a pure, colorless oil (>99% conversion based on 1 H NMR of crude product): 1 H NMR (CDCl 3 , 500 MHz) δ 2.61–2.37 (m, 3H), 1.75–1.62 (m, 2H), 1.24–0.72 (m, 9H); 13 C NMR (CDCl 3 , 125 MHz) δ 214.5, 47.1, 33.9, 25.7, 15.5, 11.2, 7.1. Spectroscopic data were consistent with that previously reported . GC analysis of ( R ) - 36 showed an er of 99:1 [determined by 20 m × 0.25 mm Chiraldex G-TA column, 70.0 °C, 15 psi, 2.9 mL/min, helium carrier gas, t R = 3.374 min, t S = 3.618 min].…”

“…With regard to the former, Koga and Meyers subsequently and independently reported the use of acyclic amino acid-derived auxiliaries in the asymmetric α-alkylation of ketones via derived imines, with good to very good diastereoselectivity in the case of cyclic ketones but poor selectivity for acyclic ketones. SAMP/RAMP dialkyl hydrazones were introduced by Enders in the late 1970s and were found to undergo alkylation with moderate to excellent diastereoselectivity, and modest to very good yield. ,, The introduction of SAMP/RAMP chemistry marked a key advance in the field of asymmetric synthesis. This method has been employed in asymmetric ketone α-alkylation but is most well-established for aldehyde α-alkylation.…”

Pathways for N-Nitroso Compound Formation: Secondary Amines and Beyond

“…Subsequent reaction of the nitrene with a further molecule of ozone would form the nitrosamine and a second molecule of oxygen (Scheme 77). 133,134 4.4. N-Nitroso Compound Formation from Organometallics.…”

Practical Kilogram Synthesis of (S)-1-Benzyl-4-Bromo-3-Methyl-1,2,3,6-Tetrahydropyridine

“…The Enders hydrazine auxiliary has been extensively utilized in organic synthesis to furnish chiral α-alkyl ketones. , In our hands, the hydrazone 2 was readily prepared and could be effectively alkylated with high stereocontrol and moderate yields. Utilizing the ( R )-1-amino-2-methoxymethylpyrrolidine (RAMP) auxiliary for C-3 methylation provided the desired ( S )-stereochemistry.…”