4573-09-5Relevant articles and documents
Regioselective Dialkylations of N-(tert-Butyl)iminocyclopentane via Deprotonating One-Pot Procedures
Knorr, Rudolf,Neuner, Brigitte
, (2018/06/04)
The title compound (1) was chosen as a model for the α/α′-regioselectivity of deprotonation and subsequent alkylation adjacent to the C=N bond. With the bulky base lithium N,N-diisopropylamide (LDA) as a catalyst, the one-pot deprotonation steps can be performed through titration with methyllithium, using gas-volumetric observation of the liberated methane. In the first step with ensuing methylation by iodomethane, the primary product is born at ?40?°C in its metastable (Z) configuration (kinetic control) and may be either isolated or converted in?situ at 30?°C into its thermodynamically favored (E)-isomer via cis to trans stereoinversion at the N-atom. Being slow enough on the laboratory time scale, this stereoinversion process can serve to control the regioselectivity of the second deprotonation/alkylation sequence as follows. The α,α′-products are formed from the intermediate (Z)-imine, whereas α,α-products result from the intermediate (E)-imine; in either case, syn deprotonation (cis to tBu at nitrogen) by LDA is apparently disfavored by the tBu group, so that anti deprotonation becomes obligatory. If a third one-pot deprotonation step is too slow with LDA, it may be performed with the stronger base butyllithium/HMPA which, however, reacts regio-unselectively. Regioselective one-pot, LDA-catalyzed deprotonation with alkylation by oxiranes (alone, or alternatingly with iodomethane) opens a short access to spiro-[2.4]heptan-4-ones.
An Organozinc Aid in Alkylation and Acylation of Lithium Enolates
Morita, Yasushi,Suzuki, Masaaki,Noyori, Ryoji
, p. 1785 - 1787 (2007/10/02)
The presence of dimethylzinc in the reaction of lithium enolates and electrophiles effectively suppresses undesired α-proton exchange reaction and enhances the efficiency of enolate alkylation and acylation.
