Isamu Arai

Aryl N- and O-trimethylsilyl substituents: reactivity toward organolithium compounds☆

Abstract The efficacy of using the trimethylsilyl group for protection of aryl amino and hydroxy substituents during reactions involving organolithium reagents has been assessed. Bromotrimethylsiloxy-benzenes or -pyrimidines reacted with n -butyl lithium by initial metal-halogen exchange followed by intra- or intermolecular rearrangement of trimethylsilyl from oxygen to the carbanionic center. Trimethysilyl groups on aryl nitrogen are stable to conditions of organolithium coupling reactions. It is suggested that for aryl 0- and aryl N-trimethylsilanes, the observed differences in reactivity at silicon are owing to the marked differences in basicity of the respective leaving groups (PhOH ⇌ Ph0-, pKA - 10, pHNH2 ⇌ PhNH−, pKA − 25).

5-Lithio-2,4-bis-O-trimethylsilyluracil rearrangement; formation of 5-trimethylsilyluracil

The lithium derivatives prepared from 5-bromo-2,4-bis-O-trimethylsilyluracil and 5-bromo-2,4-bis-NO-trimethylsilylisocytosine rearrange rapidly to form the corresponding 5-trimethylsilyl compounds, but the lithium derivative from 5-bromo-2,4-bis-NO-trimethylsilylcytosine does not.