2973-87-7Relevant academic research and scientific papers
Homoleptic zincate-promoted room-temperature halogen-metal exchange of bromopyridines
Chau, Nguyet Trang Thanh,Meyer, Maxime,Komagawa, Shinsuke,Chevallier, Floris,Fort, Yves,Uchiyama, Masanobu,Mongin, Florence,Gros, Philippe C.
experimental part, p. 12425 - 12433 (2011/01/05)
Homoleptic lithium tri- and tetraalkyl zincates were reacted with a set of bromopyridines. Efficient and chemoselective bromine-metal exchanges were realized at room temperature with a substoichiometric amount of nBu 4ZnLi2·TMEDA reagent (1/3 equiv; TMEDA=N,N,N′,N′-tetramethylethylenediamine). This reactivity contrasted with that of tBu4ZnLi2·TMEDA, which was inefficient below one equivalent. DFT calculations allowed us to rationalize the formation of N...Li stabilized polypyridyl zincates in the reaction. The one-pot difunctionalization of dibromopyridines was also realized using the reagent stoichiometrically. The direct creation of C-Zn bonds in bromopyridines enabled us to perform efficient Negishi-type cross-couplings. Mild zincation! nBu4ZnLi2·TMEDA (in substoichiometric amounts) promoted efficient and chemoselective room-temperature bromine-metal exchange of a range of bromopyridines (see scheme). DFT calculations strongly supported the formation of a stabilized tripyridylzincate, which could be reacted with electrophiles or be directly involved in palladium-catalyzed cross-coupling reactions.
Is Selective Monosubstitution of Dihalides via SRN1 Reaction Feasible? An Electrochemical Approach for Dichloroarenes
Amatore, Christian,Combellas, Catherine,Lebbar, Nour-Eddine,Thiebault, Andre,Verpeaux, Jean-Noel
, p. 18 - 26 (2007/10/02)
1,4-Dichlorobenzene and dichloropyridines undergo SRN1 reaction with various nucleophiles upon electrochemical initiation.Substitution can compete with reduction only when indirect electrolyses at low current are performed.Selective formation of monosubstitution products is observed when the nucleophiles used behave as electron-donating groups when attached to the aromatic moiety, a situation which is just the opposite of what had been observed when the same reactions were initiated photochemically.This surprising difference in behavior can be rationalized in terms of different capabilities of both activation methods to generate the key monosubstitution anion radical, ArNuX(.-).Kinetic and thermodynamic data concerning the reactivity of dichloroarenes in such processes are presented and discussed.
Novel Synthesis of 3,5-Disubstituted Pyridines by 1,4-Cycloaddition of 1-Aza-1,3-butadienes with Enamines
Komatsu, Mitsuo,Takamatsu, Shigeki,Uesaka, Masatoshi,Yamamoto, Shinji,Ohshiro, Yoshiki,Agawa, Toshio
, p. 2691 - 2699 (2007/10/02)
A new method for the synthesis of 3,5-disubstituted pyridines is described.Reactions of the N-substituted methanimines 1 with the β-substituted enamines 2 give 1-aza-1,3-butadienes 3a-3i and/or symmetrically 3,5-disubstituted pyridines 4a-c,e-h in moderate to good yields.At reaction temperatures of 150 deg C the azadienes 3 are the predominant products, and the reaction provides a good route to 1-azadienes with no substituent at the 4-position.At reaction temperatures of 200 deg C, and particularly using N-tert-butylmethanimine 1a and p-toluenesulfonic acid catalyst, the principal products are symmetrically 3,5-disubstituted pyridines.The cycloaddition was shown to proceed via the azabutadiene intermediate 3.Reactions of 3 with the enamines 2 lead to unsymmetrically 3,5-disubstituted pyridines.The mechanisms of these cycloadditions are discussed.
