Di-Grignard reagent

FIGURE 77. Molecular geometry of the 1,1-di-Grignard reagent 169 in the solid state... 

A munber of 1,1-di-Grignard reagents have been reported, including CH2(MgX)2 (X = Br, I, from the dihalide and Mg/Hg), and (43). Pyrolyzes of Mc2Mg and Me2Be produce polymeric (MCH2). 

For formation of 1,2-dilithio compounds and 1.2-di-Grignard reagents, but not by this method, see van Eikkema Hommes Bickelhaupt Klumpp Reel. Trav, Chim. Pays-Bas 1988, 107. 393. Angew. Chem. Ini. Ed. Engl. 1988, 27. 1083 [Angew. Chem. 100, 1100],... 

A system with two cyclohexasilanyl substituents on one phenyl ring is obtained from the phenyl- 1,4-di-Grignard reagent and ClSigMen83,84 (equation 17). 

The 1,4-di-Grignard reagent prepared from 1,4-dibromobutane was used for the preparation of 1-phenyl-tetrahy-droarsole 47 by reaction with phenylarsenic dichloride (Equation 5) <2001JIC224>. 

For formation of 1,2-dilithio compounds and 1,2-di-Grignard reagents, but not by this method, see van... 

Solvent effects were more dramatic for the 1,5-di-Grignard reagent 9 [31]. In THF, the equilibrium constant for conversion of l,5-di(bromomagnesio)pentane 9 to magnesiacyclohexane 10 and magnesium dibromide was determined as 299 + 31 (AH = +2 kcal mol , AS=+17 eu). In diethyl ether, the equilibrium lies completely toward l,5-di(bromomagnesio)pentane 9. 

Typically, attempts to synthesize 1,2-di-Grignard reagents from 1,2-dihaloalkanes fail, because metal halide elimination after insertion of the first magnesium atom is faster than formation of a second magnesium-carbon bond. The only l,2-di(halomagnesio)alkane [16] synthesized in the classic fashion is a l,2-di(bromomagnesio)cyclopropane 22 [Eq. 

Application of the purified magnesium method to l,3-dibromo-2,2-dimethylpropane affords 15 18% of 1,3-di-Grignard reagent [23], which has been reacted with two molecules of cyclohexanone to afford the expected 1,3-diol [24]. However, the substitution pattern of the 1,3-di-Grignard reagent is limited one /i-alkyl substituent resulted in low yields and high decomposition rates owing to increased / -hydride mobility [25]. 

A 1,5-di-Grignard reagent 100 can be formed from disulfone 99 by removal of the protons a to the sulfonyl groups with ethylmagnesium bromide as base [Eq. (40) 77]. The reagent reacts with ketones or bromine to afford diadducts in low yields. 

Compound 24 is formally j 1,3-di-Grignard reagent [see Seeiion I 1.4.2) and has proven useful lor the preparation of a number o l.3-dimc(ulla-cNclohul.mcs 31 nf Groups 4 and 14 117a (Scheme II.M). Reunion of 24 wiili silicon tetrachloride gave die spiro compound 32 2K. ... 

The parciu 1.2-di-Grignard reagent 36 has been obtained in lOV. yield from the reaction of... 

Finally, il should be pointed out that 49. the double magnesium bromide salt of acetylene, is also a 1.2 di Grignard reagent, even though it... 

Other 1,3-di-Grignard reagents arc rare. In the aliphatic series. 63a, b arc the only other representatives (Scheme 11.21). The expectation that the yields of 63 in the direct reaction from 62 would be substantially higher because of higher strain in ihe bicyclic elimination products 64 was not fulfilled the yields were 7Vt (63a) and < 45 /< (63b) 40. ... 

Similarly, a number of meiallacyclobuianes (78— 85) of iransilion metals were obtained from 60b (Scheme 11,26). In this context, Ihc synthesis of 31 and 32 from the formal 2-iitana-1,3-di-Grignard reagent 24 (Scheme 11.11) should also be mentioned. 

Organobis(cupratesY, spiroannelation.16 1,4-Dilithiobutane, prepared from 1,4-dichlorobutane and lithium in ether at 0°, on reaction with copper thiophenoxide (2 equiv.) forms a biscuprate, formulated as 1 for convenience. This dimetallic reagent adds to 3-halo-5,5-dimethyl-2-cyclohexenones (2) to form the spiro-[4.5]decanone 3 in yields as high as 96%. Cuprates prepared from other Cu(I) sources are less efficient, as is the cuprate prepared from di-Grignard reagents... 

This synthesis can be extended to di-Grignard reagents (equation 1). 

---