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v) NHMDS (1.1 eq), -78“Cto rt, 16 h
Ex: R- Me « = 4 72%
Et «= 5 63%
Sulfur-stabilized copper-zinc carbanions have been used  by Knochel et al. A first type obtained from the reaction of the Simmons-Smith reagent with a copper(i) thiolate was treated with a
reactive electrophile as shown.
ICHjZnl + RSCu -----------> [ RSCH2Cu:Znl2 ]
R = n-CjoHji
Insertion of a methylene unit between the nucleophile thiolate and the electrophile was thus realized.
A second type of such an organocopper-zinc reagent was prepared, and reacted as shown in the accompanying scheme .
22.214.171.124 a-Metallated sulfides
In view of the synthetic applications, among carbanions stabilized by only one divalent sulfur alum, allylic thiocarbanions proved to be particularly valuable, as shown with Biellmann coupling of allylic groups, applied to an elegant synthesis of squalene from farnesyl bromide . In this synthesis, the retention of the allylic double bond position and stereochemistry in both the metallation-alkylation and the desulfurization steps are noteworthy. However, the results are not always as clear-cut, and
il) CuCN, 2 LiCl
a discussion of modifications introduced to the initial Biellmann’s procedure, together with examples of applications, can be found in Block’s monograph .
We owe to Corey and Seebach  an efficient procedure for the generation of phenylthiomethyllithium (PhSCH2Li), opening the way for practical applications. They found that this reagent was produced in about a 97% yield through reaction of equimolar amounts of n-butyllithium, DABCO and thioanisole in THF at 0°C for 45 min.
PhSMe +¦ n-BuLi ------ÐÀÂ(Ó»> PhSCH,Li
Preparation of a solution of phenylthiomethyllithium
To a solution of DABCO (3.369 g, 30 mmol) and thioanisole (3.726 g, 30 mmol) in THF (45 ml), stirred under nitrogen at 0°C, was added n-butyllithium (32 mmol) in n-hexane within 12 min. A complex which precipitated, dissolved upon warming to room temperature to give a pale-
yellow solution of the reagent with a yield of about 97% as shown by deuteration and NMK analysis.
From  with permission.
In the same paper the authors reported the preparation of a THF solution of bis(phenylthio)methyllithium. The lithio derivative is formed almost instantaneously and quantitatively (deuteration and NMR analysis).
(PhS)2CH2 + n-BuLi ------------> (PhS)2CHLl
To a solution of bis(phenylthio)methane (2.324 g, 10 mmol) in THF (20 ml) stirred under nitrogen at 0°C, was added n-butyllithium (10mmol) within 7 min to afford a clear yellow solution of the lithium compound, which can be used for reaction after 10 min and which is stable at 0°C for at least 12h.
From  with permission.
The two schemes showing homologation of halides through alkylation of phenylthiomethyllithium as the key step for carbon-carbon bond formation illustrate the potential of this reagent .
Me(CH2)8CH2I ------------------> Me(CH2)8CH2CH2I
28 2 il) Md / DMF
I) PhSCHjLl U) Mel / DMF Ø) Nal
Application to methylidenatiou and epoxide formation will be described in Section 4.4.1.
Methylthiomethyllithium was prepared by Peterson  from the reaction of dimethyl sulfide with the (TMEDA)-n-butyllithium complex. Subsequent reaction with benzaldehyde afforded the corresponding alcohol in an 84% yield.
Alkylthio compounds containing metal coordinating groups inside the molecule in order to enhance the stability as well as the nucleophilicity of the organolithium derivative have been prepared . An example is given here, together with some other a-lithiated sulfides generated by metallation and which are illustrative of the versatility of the process.
These reagents were introduced, respectively, by Meyers , Oshima , Trost  and Corey , and skillfully applied as shown in the syntheses of cyclobutanones  and a-unsaturated aldehydes , in which the initially formed carbon-carbon bond was the first step of the overall synthetic schemes elaborated.
Ogura  has more recently introduced 3-methylthio-2-propenyl p-tolyl sulfone, available through successive reactions of 1,3-dichloropropene with sodium p-toluenesulfinate and sodium