Magnesium dibromide

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. 

Allenylstannanes add to aldehydes in the presence of equimolar boron trifluoride etherate, or magnesium dibromide etherate to give homopropargyl alcohols.37 If the aldehyde has a branched alkyl group, the syn adduct is formed (equation 9-43) through... 

The dianion (62 Scheme 35), prepared from alkenethiols, gives good y-selectivity toward both alkylation and carbonyl addition. The y-products (enol sulfides) may be converted to dimethylacetals by treatment with mercury(II) chloride in methanol. When (62) is associated with magnesium dibromide, the addition of carbonyl compounds produces the a-adducts with regioselectivity greater than 90%. The reaction with methyl vinyl ketone, followed by a Cope rearrangement, results in reattachment at the original y-position. 

Finally, 144 is an exotic example involving a completely different application of a cyclic dior-ganylmagnesium compound it was derived from the di-Grignard reagent 104 (Scheme 11.30) by removal of magnesium dibromide with dioxane and used for the formation of the unique metallacyclic catenane 145 (which is in equilibrium with its side-on coordinated analogue) [64] (Scheme 11.42). 

CioH4oBr2MgN2oOiOf Hexakis(urea)magnesium dibromide tetrakis(urea), 45B, 783... 

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