Structure of a Chiral Lithium Azaenolate: Monomeric, Intramolecular Chelated Lithio‐2‐acetylnaphthalene‐SAMP‐hydrazone

Abstract

A more detailed insight into the structure of the 1‐azaallyl anion of a SAMP‐hydrazone has been made possible by the first X‐ray crystallographic study of a chiral monomeric azaenolate. The lithiated 2‐acetylnaphthalene‐SAMP‐hydrazone 1 exists as rubyred crystals; it has an η1‐structure with intramolecular methoxychelatization, while the lithium ion is solvated by two THF molecules.

Thermodynamically Favored Anion Rearrangements in Li and Na Complexes of (S)-N-α-(Methylbenzyl)allylamine

“…One important variable that can provide for unexpected outcomes is base-induced changes in the anion structure or form. Metal-promoted anion rearrangements are common and widely reported, − an important example being the [1,2] and [2,3] Wittig sigmatropic rearrangement, which has found wide range application in the base-promoted synthesis of homoallylic alcohols from allyl ethers. − In studying such phenomena, Fraenkel and co-workers have established that allylic anions can undergo facile rearrangements. , Deprotonation and subsequent coordination by a Li cation can allow delocalization within the allylic anion, the extent influenced by the degree of solvation. Resonance stabilization and the presence of the metal mean that such anionic rearrangements can be thermodynamically favored.…”

2-Azaallyl Anions, 2-Azaallyl Cations, 2-Azaallyl Radicals, and Azomethine Ylides

“…To rationalize this remarkable stereochemical outcome, Pearson and co-workers proposed a transition state structure in which the interaction of the methoxy group in the auxiliary with the lithium cation plays a critical role in determining both the geometry of the starting 2-azaallyl anions and the facial selectivity of the cycloaddition (Scheme , inset). Such a model is reminiscent of that involved in Enders’ SAMP hydrazone chemistry …”

“…Such a model is reminiscent of that involved in Enders' SAMP hydrazone chemistry. 157 As a follow-up to their pioneering work in the field, Pearson's group systematically investigated the reactions between heteroatom-substituted 2-azaallyl anions generated by Li−Sn exchange with conjugated polyenes. 29 For example, the heteroatom-substituted cyclic 2-azaallyl anions from 208b and 208a underwent [4π + 2π] cycloaddition with cyclohexadiene to afford azabicyclic compounds 214 and 215/215′, respectively, in decent yields and selectivities (Table 8).…”

(S)-1-Amino-2-methoxymethylpyrrolidine

“…16 The structure of a chiral lithium SAMP hydrazone azaenolate has been determined. 17 In cases where SAMP did not lead to satisfactory inductions, a modified auxiliary, (S)-1-amino-2-dimethylmethoxymethylpyrrolidine (SADP), 18 enhanced the stereochemical control. The SAMP hydrazone method is valuable for the stereoselective alkylation of ketones and aldehydes.…”