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7.6.10.5 Method 5: Reaction of Alkoxyalkyl Halides or Their Analogues with Magnesium

DOI: 10.1055/sos-SD-007-00542

Oshima, K.Science of Synthesis, (20047587.

Grignard reagents can be prepared from chloromethyl ethers by reaction in tetrahydrofuran or dimethoxymethane at 30 to 20°C. These reagents decompose, forming ethene and alkoxy­magnesium chloride at temperatures >15°C, but the thermal stability is ­enhanced in hexamethylphosphoric triamide, and increases in the order R1=Me < Et < iPr < Bn CH2CH2Cl, the latter compound being stable at room temperature (Scheme 26).[‌48‌,‌49‌] Functional substituents in the 2-position usually undergo ready elimination on attempted Grignard formation, as shown in Scheme 27 with, for example, Y=OR1, SR1, NR12, or PR12.[‌50‌] In compounds where such elimination is not favored, however, stable Grignard reagents 20[‌51‌] and 21[‌52‌] can be formed; the perfluoro derivative 22[‌53‌] has additionally been reported (Scheme 28). It has been possible to prepare [(dialkylamino)ethyl]magnesium derivatives [Mg(CH2CH2NR12)Cl] in tetrahydrofuran at 100 to 75°C using highly activated magnesium, and these compounds decompose in the temperature range 90 to 20°C by elimination of ethene, with the stability increasing in the order NR12=NMePh < NPh2 < NCy2.

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