Abstract
The reaction of different 1-chloro-n-phenylsulfanylalkanes 5 with 2 equivalents of lithium naphthalene at -78 oC followed by addition of a carbonyl compound (Bu t CHO, Et2CO, (CH2)5CO) leads, after hydrolysis with water, to the expected sulfanyl alcohols 8 through a selective lithiation of the carbon-chlorine bond. When an excess of lithium (1:4 molar ratio) is added to the reaction mixture before the hydrolysis and the system is allowed to reach -50 oC during 1.5 h, lithiation of the remaining carbon-sulfur bond takes place. The addition of a second carbonyl compound (Bu t CHO, PhCHO), followed by hydrolysis, gives differently substituted diols 3.
Highlights
The reaction of dilithium compounds[1] with electrophiles allows the preparation of difunctionalized molecules in a single synthetic operation. The stability of these intermediates, which exhibit fascinating structures, depends mainly on the relative position of the lithium atoms and on the hybridization of the carbon atoms bonded to the metal. They are accessible by applying the same methodologies as for single organolithium compounds,[2] such as deprotonation reactions, halogen–lithium exchange, reductive cleavage of ethers and thioethers with lithium metal, and transmetallation process principally
Bromo-n-chloroalkanes 1 (X = Br) in the presence of a carbonyl compound to give functionalized alcohols 2.5 This process has to be performed at low temperature using a stoichiometric amount of the lithiating reagent and in the presence of the electrophile (Barbier-type reaction conditions6) in order to avoid the decomposition of the highly reactive 1-chloro-n-lithioalkane intermediate initially formed
In the context of our continuing interest in the dilithiation of different 1,n- difunctionalized compounds, we report here the selective mono- and dilithiation of a number of 1-chloro-n-phenylsulfanylalkanes[8] and their use as dianionic synthetic equivalents in the reaction with different carbonyl compounds as electrophiles
Summary
The reaction of dilithium compounds[1] with electrophiles allows the preparation of difunctionalized molecules in a single synthetic operation.
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