Publication

Fluorophenols and (trifluoromethyl)phenols as substrates of site-selective metalation reactions: to protect or not to protect

Manfred Schlosser
2001
Journal Articles

Abstract

O-Methoxymethyl (MOM) protected fluorophenols can be cleanly metalated and subsequently be submitted to site-selective electrophilic substitution. The 2- and 4-isomers exhibit ambivalent reactivity: deprotonation occurs at the position adjacent to the O when butyllithium is employed whereas the position adjacent to the F is attacked by the superbasic mixt. of butyllithium and K tert-butoxide (LIC-KOR). The MOM-protected (trifluoromethyl)phenols react exclusively at O-neighboring positions. The meta isomer provides another example of optional site selectivity, undergoing H/metal exchange at the 2-position with the LIC-KOR reagent and at the 6-position with sec-butyllithium. Unprotected (trifluoromethyl)phenols can also be ortho-metalated after O-deprotonation, although the products are formed in only moderate yields. [on SciFinder (R)]

Official source

https://infoscience.epfl.ch/entities/publication/1c1b4f95-aec6-4372-b840-f6206d9c344c

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Manfred Schlosser
2001
Journal Articles

Abstract

Official source

https://infoscience.epfl.ch/entities/publication/1c1b4f95-aec6-4372-b840-f6206d9c344c

About this result

Related concepts (19)

Organolithium reagent

In organometallic chemistry, organolithium reagents are chemical compounds that contain carbon–lithium (C–Li) bonds. These reagents are important in organic synthesis, and are frequently used to transfer the organic group or the lithium atom to the substrates in synthetic steps, through nucleophilic addition or simple deprotonation. Organolithium reagents are used in industry as an initiator for anionic polymerization, which leads to the production of various elastomers.

Protecting group

A protecting group or protective group is introduced into a molecule by chemical modification of a functional group to obtain chemoselectivity in a subsequent chemical reaction. It plays an important role in multistep organic synthesis. In many preparations of delicate organic compounds, some specific parts of their molecules cannot survive the required reagents or chemical environments. Then, these parts, or groups, must be protected. For example, lithium aluminium hydride is a highly reactive but useful reagent capable of reducing esters to alcohols.

Metal–halogen exchange

In organometallic chemistry, metal–halogen exchange is a fundamental reaction that converts an organic halide into an organometallic product. The reaction commonly involves the use of electropositive metals (Li, Na, Mg) and organochlorides, bromides, and iodides. Particularly well-developed is the use of metal–halogen exchange for the preparation of organolithium compounds. Two kinds of lithium–halogen exchange can be considered: reactions involving organolithium compounds and reactions involving lithium metal.