Magnesiated preparation

Bach has used the selective exchange reaction on 2,4-dibromothiazole for the synthesis of substituted 4-bromothia-zoles.59,59a Lithium magnesiates, prepared by the reaction of an organolithium reagent (2 equiv.) and an... 

Tetraalkyl-9,10-dihydrodistannaanthracenes 4 have been prepared via the lithiation73 or the magnesiation of 1,2-dibromobenzene,166 followed by reaction with R2SnCl2. The tetramethyl derivative is butterfly shaped with a dihedral angle of 142°, but the tetra-/-butyl derivative is planar.73 The stannepin 5 and stannolane 6 were obtained as byproducts of the former reaction. 

Magnesiated triazene derivatives like 96 can further be used for the preparation of functionalized carbazoles 97 (equation... 

Synthesis of copolysiloxanes 14, a candidate for dental and medical devices and sensors, required the preparation of the substituted allylbenzene 13 (Scheme 20) °. However, attempted cross-coupling reaction of 12 with allylzinc bromide resulted in failure. Alternatively, the magnesiation of 12 with lithium tributylmagnesate followed by the addition of allyl bromide provided 13 in excellent yield. 

Sapountzis, I. Dohle, W. Knochel, P. Stereoselective preparation of highly functionalized (Z)-3-magnesiated enoates by an I-Mg exchange reaction. Chem. Commun. 2001, 2068-2069. 

Extensive studies have been made of the metallation of 1-alkynes by organomagnesium compounds [D], For preparative purposes, metallation by Grignard reagents (commonly ethylmagnesium bromide) in diethyl ether or THF is usually straightforward and convenient. Magnesiation of acetylene itself has special features and is described separately. 

Lactone synthesis. This Ti(II) complex can serve as catalyst for hydro-magnesiation of allylic or homoallylic alcohols, prepared by addition of vinyl- or allyl-Grignard reagents to ketones. Ethylmagnesium bromide is used as the source of magnesium hydride. The carbonylation of the organomagnesium intermediate results in a -y- or a 5-lactone (equation I). 

The sUylation of aromatic or heteroaromatic compounds can be performed via magnesiated or lithiated intermediates, which can be accessed by hydrogen-metal or halogen-metal atom exchange. Thus, C-4 silylation of imidazoles is achieved from4-iodo imidazoles (eq 45), while C-2 silylated oxazoles are prepared by addition of TMSOTf to the lithiated oxazole (eq 46) interestingly, for this reaction, the employment of TMSCl as electrophile... 

Arynes prepared from the aryl iodides 57 via 2-magnesiated aryl sulfonates 58 have been reported to undergo nucleophilic addition by magnesium thiolates [45], amides [45] or phenylselenide [46], giving rise to ortho-thio, amino, or seleno-substituted arylmagnesium species 59-61, respectively (Scheme 12.21). These arylmagnesium intermediates can be trapped in situ by various electrophiles, such... 

Scheme 4.14 Preparation of diaryl- and diheteroarylzinc reagents by direct magnesiation with TMP2Zn-2 MgC. 2 LiCI [78].

Scheme 5.4 Preparation of C(sp )-organomagnesium reagents by direct magnesiation with TMPMgCI-LiCI [29-31].

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