Chemistry of Conversions of [o-[1-Halo-1-(p-tolylsulfonyl)alkyl]benzyl]trimethylsilanes to o-Quinodimethanes and Benzocyclobutenes
journal contributionposted on 17.03.1998 by Brian D. Lenihan, Harold Shechter
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Trimethyl[o-[bromo(p-tolylsulfonyl)methyl]benzyl]silane (10) is prepared from o-[(trimethylsilyl)methyl]benzyl p-tolyl sulfone (9), n-BuLi, and bromine. Sulfone 9 eliminates trimethylsilyl bromide upon reaction with TBAF in acetonitrile to give the presumed intermediate, α-sulfonyl-o-quinodimethane 11, which (1) dimerizes to disulfone 12 and (2) is trapped by alkyl fumarates to yield (p-tolylsulfonyl)tetrahydronaphthalenes 17a,b and 18a,b, respectively. Sulfone 9 is converted by n-BuLi and alkyl halides to α-alkyl-α-bromosulfones 19a−f which react with TBAF to give α-sulfonylbenzocyclobutenes 21a−f and vinyl sulfones 23a−f, apparently upon ring closure and upon 1,5-sigmatropic rearrangements of hydrogen in α-sulfonyl-o-quinodimethane intermediates 20a−f and 22a−f. Further, sulfone 9, n-BuLi, and tert-butyl hypochlorite yield α-chlorosulfone 26 and α,α-dichlorosulfone 27. TBAF effects dechlorotrimethylsilation of 27 to chloro(p-tolylsulfonyl)cyclobutene 28 presumably upon formation and cyclization of o-quinodimethane 29. Silanes 10, 19a−f, and 27 are therefore practical synthons for o-quinodimethane intermediates 11, 20a−f and 22a−f, and 29 respectively.