Page 660 - Advanced Organic Chemistry Part B - Reactions & Synthesis

HMPA can accelerate the reaction and improve yields when electron transfer is a 635
complication. 77
SECTION 7.2
n -C H I Reactions of
7 15
Organomagnesium and
N Li HMPA N (CH 2 6 3 80% Organolithium
) CH
Compounds
CH NC(CH 3 ) 3 CH NC(CH 3 ) 3
Organolithium reagents in which the carbanion is delocalized are more useful than
alkyllithium reagents in alkylation reactions. Allyllithium and benzyllithium reagents
can be alkylated and with secondary alkyl bromides and a high degree of inversion of
configuration is observed. 78
CH CH 2 CH CH 3
3
2
C PhCH C
PhCH Li 2 CH 3
2
H 3 C Br
H H
58% yield
100% inversion
Alkenyllithium reagents can be alkylated in good yields by alkyl iodides and
bromides. 79
CH 3 CH 3 CH 3 CH 3
1) Li
C C C C
(CH ) I
2) CH 3 2 3
Br H CH (CH ) H
2 3
3
The reactions of aryllithium reagents are accelerated by inclusion of potassium
alkoxides. 80
F
F KOt Bu
THF H
H Br
Li + C 2 5 C 2 5
–70°C
75%
Alkylation by allylic halides is usually a satisfactory reaction, and in this case the
14
reaction may proceed through a cyclic mechanism. 81 For example, when 1- C-allyl
chloride reacts with phenyllithium, about three-fourths of the product has the labeled
carbon at the terminal methylene group.

CH
*
H C CH 2 *
2
PhCH CH CH 2
2
Ph Cl
Li
77 A. I. Meyers, P. D. Edwards, W. F. Rieker, and T. R. Bailey, J. Am. Chem. Soc., 106, 3270 (1984);
A. I. Meyers and G. Milot, J. Am. Chem. Soc., 115, 6652 (1993).
78 L. H. Sommer and W. D. Korte, J. Org. Chem., 35, 22 (1970).
79
J. Millon, R. Lorne, and G. Linstrumelle, Synthesis, 434 (1975).
80 L. Brandsma, A. G. Mal’kina, L. Lochmann, and P. v. R. Schleyer, Rec. Trav. Chim. Pays-Bas, 113,
529 (1994); L. Lochmann and J. Trekoval, Coll. Czech. Chem. Commun., 51, 1439 (1986).
81
R. M. Magid and J. G. Welch, J. Am. Chem. Soc., 90, 5211 (1968); R. M. Magid, E. C. Nieh, and
R.D.Gandour,J.Org.Chem.,36,2099(1971);R.M.MagidandE.C.Nieh,J.Org.Chem.,36,2105(1971).