Directing metalation group

For conversion of functionalized diorganozincs into tertiary amines, aromatic compounds which contain a directed metallation group, such as Af,Af-dialkylbenzamides, methoxymethyl phenyl ether, phenyl oxazolines and phenyl Af,Af-dialkylcarbamates, were ortho-lithiated, transmetallated and then aminated with 2a in good yields, but with a slower reaction rate (Scheme 19). 

According to NMR data, reaction of lithium tetramethylpiperidine (TMP) and t-Bu2Zn, in a 1 1 molar ratio (Scheme 6) affords the heteroleptic zincate [f-Bu2Zn(TMP)]Li (36) . An interesting feature of this compound is that it is capable of metalate arenes that contain a directing metalating group (DMG) in ortho-posilion and thus allow further derivatization by reaction of the zincate intermediate with electrophiles (E+). 

Regioselective substitution reactions of a series of 2- and 3-hydroxybiaryls including BINOL have been performed via a new directed orf/io-metallation procedure.75 O-Aryl AMsopropylcarbamates, conveniently prepared from phenols and isopropyl isocyanate, have been temporarily and in situ N-protected by means of silyl inflates to form stable intermediates for low-temperature lithiation reactions using n-BuLi-TMEDA in diethyl ether. The IV,IV-dialkyl aryl O-sulfamate has been reported as a new directed metallation group.76... 

DMG, Directed Metalation Group EWG, electron-withdrawing group. 

Certain derivatives of benzene and naphthalene can be lithiated with sec-butyllithium (sec-BuLi). This reaction is regioselective. It takes place exclusively in the ortho-position (Directed ortho Metalation, DoM) to a so-called Directed-Metalation Group (DMG), whose presence, accordingly, is a prerequisite for such a metalation. Figure 5.37 gives examples of DMGs that are bound through a C, an O, or an N atom to the aromatic compound. 

The concurrent and independent discovery of DoM by Wittig and Gilman over sixty years ago set the stage for the systematic work of Hauser, which was pursued in a number of laboratories in the late 1970s and has led to the current status of Directed Metalation Groups (DMGs), which allow the regioselective ortho introduction of a host of electrophiles (Scheme 2) [9a-c],... 

Metallinos, C., Nerdinger, S., Snieckus, V. N-Cumyl Benzamide, Sulfonamide, and Aryl O-Carbamate Directed Metalation Groups. Mild Hydrolytic Lability for Facile Manipulation of Directed Ortho Metalation Derived Aromatics. Org. Lett. 1999, 1, 1183-1186. 

Substrate—Aromatic bromides or iodides (Ar-X) are rapidly converted to the corresponding aryllithium (Ar-Li) when treated with 1 molar equivalent of n-BuLi or 2 molar equivalents of (-BuLi. However, some substrates may rearrange to a more thermodynamically stable aryllithium via abstraction of a proton from a more acidic site, and this can lead to the formation of unwanted impurities (Scheme 12.5, eq. 2). Similarly, proton abstraction from aryl bromide substrates that contain an ortfto-directing metalation group (DMG) may lead to impurities in the final product. ... 

This coupling can be extended to a synthesis of m-quinqucaryls by using a 1,3-dihalobcnzcne substituted at C2 by a directing metalation group CON(C2H5)2, CN OMOM, or NH2. 

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