Thianthrene lithiation

A completely different reaction to give 1,2-dilithio synthons was performed by double lithiation of thianthrene 426 (Y = S) under catalytic conditions. Thus, after the first lithiation with lithium and DTBB (4%) in THF at —90 °C, the corresponding intermediate (of... 

Dibenzo[6,e][l,4]dioxin, phenoxathiin and thianthrene all react with butyllithium with proton abstraction from a benzene ring. Dibenzo[f ,e][l,4]dioxin and thianthrene are metallated at the 1-position (128), while lithiation of phenoxathiin occurs ortho to the C—O bond rather than the C—S bond, i.e. at C-4, (129). The lithiated products provide excellent intermediates for functionalizing the rings at these positions, usefully complementing the product distribution pattern in electrophilic substitution reactions. 

Dibenzothiepines 71 can also be accessed readily from thianthrene 70 by lithiation and subsequent reaction with electrophiles, hydrolysis and acid-catalysed cyclisation <03T2083>. 

The DTBB-catalyzed lithiation of 4-hetero-substituted dibenzothiins (68), such as phenoxathiin (68a), phenothiazine (68b) and thianthrene (68c), at low temperature gives the corresponding functionalized organolithium intermediates (69), which by reaction with different electrophiles afford, after hydrolysis, the expected functionalized... 

The reductive opening of thianthrene (68c) has been reported in Section IV.C for homologation purposes. However, the lithiation of (68c) and reaction with appropriate electrophiles led to other interesting organic compounds. Thus, after the reductive opening lithiation of (68c) and reaction with a carbonyl compound as the... 

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