Reactivity of Benzylic Carbanions. 10. Rearrangement of the Me3SI Group in 9,9-Bis(trimethylsilyl)- and 9-Alkyl-9-(trimethylsilyl)-10-lithio-9,10-dihydroanthracenes

Article abstract of DOI:10.1021/jo00173a052

A <1,4> Me3Si migration has been shown to occur in 9,9-bis(trimethylsilyl)-10-lithio-9,10-dihydroanthracene (C1); the resulting carbanion (C2), protonated by H2O, gives rise exclusively to the cis-9,10-bis(trimethylsilyl)-9,10-dihydroanthracene ((Me3Si)2DHA) in high yield.The same migration was also observed in a series of 9-(trimethylsilyl)-9-alkyl-10-lithio-9,10-dihydroanthracenes (alkyl = Me, Et, i-Pr), which were transformed into a mixture of cis and trans 9,10-disubstituted DHAs (VII, VIII, IX).Experimental evidence was obtained for an intramolecular shift, and the mechanism of the reaction was considered, particularly the possibility of a reversible Me3Si migration (C2 -> C1).The driving force of the Me3Si shift is believed to involve easy formation of pentacoordinated silicon derivatives combined with relief of strain in, and formation of, more stable ion pairs.In light of these results, the rearrangements observed in 9-(trimethylsilyl)-9-deuterio-10-lithio-9,10-dihydroanthracenes were reexamined.A comparison with other well-known R3Si migrations in carbanions, mainly in systems containing heteroatoms, was made, and the structural requirements to observe such reactions in genuine carbanions were delineated; the DHA substrate appears to be well suited for this rearrangement.