Page 661 - Advanced Organic Chemistry Part B - Reactions & Synthesis

636 Coupling of certain lithiated reagents with aryl and vinyl halides is also possible. 82
These reactions probably proceed by a fast halogen-lithium exchange, generating the
CHAPTER 7
alkyl halide, which then undergoes substitution. This reaction has been applied to
Organometallic
-lithiobenzamides. 83
Compounds of Group I
and II Metals O
–
O Li +
+ Br OCH 3 Ph NHCH CH
Ph NCH CH Li 2 2 OCH 3
2
2
91%
Intramolecular reactions are useful for forming small rings. The reaction of 1,3-,
1,4- , and 1,5-diiodides with t-butyllithium is an effective means of ring closure, but
1,6-diiodides give very little cyclization. 84
CH 2 I
t -BuLi
CH I
2
97%
Functionalized organolithium reagents can be prepared and alkylated. The config-
uration of the dioxanyl reagent 2 proved to be subject to control. 85 The kinetically

favored trans lithio derivative is converted to the more stable cis isomer at 20 C. Both
isomers were methylated with retention of configuration at saturated carbon.
CH (CH ) SPh CH (CH ) Li
2 5
3
3
2 5
Li naphthalenide CH (CH ) Li
3
2 5
O O –20°C
–78°C O O O O
2
CH(CH )
3 2
CH(CH ) CH(CH )
3 2
3 2
Both trialkylsilyl and trialkylstannyl halides usually give high yields of substi-
tution products with organolithium reagents, and this is an important route to silanes
and stannanes (see Section 9.2.1 and 9.3.1).
Grignard reagents are somewhat less reactive toward alkylation but can be of
synthetic value, especially when methyl, allyl, or benzyl halides are involved.
CH 3 CH 3 CH 3 CH
Br 3 CH CH CH
1) Mg 2 2
2) CH 2 CHCH Br
2
CH
CH 3 3 CH CH 3
3
79% Ref. 86
Synthetically useful alkylation of Grignard reagents can also be carried out with alkyl
sulfonates and sulfates.
PhCH MgCl + CH CH CH CH OSO C H PhCH 2 CH 2 CH 2 CH 2 CH 3
2
3
2
2 7 7
2
2
50–59%
Ref. 87
82
R. E. Merrill and E. Negishi, J. Org. Chem., 39, 3452 (1974).
83 J. Barluenga, J. M. Montserrat, and J. Florez, J. Org. Chem., 58, 5976 (1993).
84
W. F. Bailey, R. P. Gagnier, and J. J. Patricia, J. Org. Chem., 49, 2098 (1984).
85 S. D. Rychnovsky and D. J. Skalitzky, J. Org. Chem., 57, 4336 (1992).
86 J. Eustache, J.-M. Barnardon, and B. Shroot, Tetrahedron Lett., 28, 4681 (1987).
87
H. Gilman and J. Robinson, Org. Synth., II, 47 (1943).