Halogen–lithium exchange versus deprotonation: regioselective mono- and dilithiation of aryl benzyl sulfides. A simple approach to α,2-dilithiotoluene equivalents
reactions between aryl benzyl sulfides and alkyllithiums were investigated. The resultant mono- and dilithiated intermediates were converted into the corresponding aldehydes and boronic, or carboxylic acids in good yields. It was found that diethyl ether stabilizes the ortho-lithiated compounds toward isomerisation to the benzylic derivatives. The process occurs easily in THF at low temperature and is
an alkyl- lithium to 1-phenylthio-1-trimethylsilylethene (7), and transmetallation of a tributylstannyl moiety. The formation of an alkyl-lithium by reaction of lithium naphthalenide with a phenyl sulphide provided an additional route to (2) from bis(phenylthio)acetals (8). An alternative path to the α-phenylthiosilanes (2) was to reduce the corresponding α-phenylsulphonylsilane (15); these, in turn