- Alkyl-substituted allylic lithium compounds: Structure and dynamic behavior
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Several methyl-substituted allylic lithium compounds have been prepared by CH3Li cleavage of their corresponding bis(methyl)bis(allylic)stannanes. Low-temperature 13C and proton NMR studies of 1:1 complexes of these allylic lithium compounds with TMEDA establish their structures. NMR line shape changes with temperature provide barriers to rotation. Results are listed in order as follows (allyl substituents, compound number, barrier to rotation in kcal·mol-1, and bonds undergoing rotation): 1,1-dimethyl, 26, 18, 2-3; endo-1-methyl, 27, 19, 2-3; endo-1-exo-3-dimethyl, 28, 21, 1-2 and 2-3. These observations together with the allylic 13C NMR chemical shifts indicate that in the case of unsymmetrical alkyl substitution at the termini the allyl C-C bond to the more substituted terminus is of higher bond order than that to the less substituted terminus. Unsymmetrical substitution is proposed to reduce the degree of delocalization compared to the symmetrically substituted allylic lithium compounds. A mechanism is proposed for the rotation process which is consistent with the Eyring activation parameters.
- Fraenkel,Qiu
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p. 12806 - 12812
(2007/10/03)
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- REACTIONS OF TRIMETHYLTINSODIUM WITH ALKYL HALIDES. EFFECTS OF STRUCTURE AND SOLVENT ON COURSE OF REACTION AND REACTIVITY
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The reactions of eleven alkyl chlorides and bromides with trimethyltinsodium have been examined.It has been found that primary and secondary halides react smoothly and rapidly to provide good yields of substitution products in THF and TG at Oo.The reaction is less satisfactory for allyl bromide and unsatisfactory for cinnamyl chloride and tertiary halides.Trimethyltinsodium and 2-chlorobutane react with second order kinetics.Relative reactivities of the halides have been determined in the two solvents and are discussed.Lithium, sodium and potassium as counterions yielded the same results in the reaction of the trimethyltinalkils with primary, secondary and tertiary butyl bromides in THF.
- Kuivila, Henry G.,Reeves, William G.
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p. 801 - 808
(2007/10/02)
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