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.
Use of o-[(trimethylsilyl)methyl]benzyl
p-tolyl sulfone (3) for synthesis and
cycloaddition of
substituted o-quinodimethanes has been investigated.
Sulfone 3 is prepared from 2-methylbenzyl
alcohol (4) by reactions with n-BuLi and
chlorotrimethylsilane to form
o-[(trimethylsilyl)methyl]benzyl alcohol (7) which phosphorus tribromide converts to
o-[(trimethylsilyl)methyl]benzyl
bromide
(8). Displacement of 8 with sodium
p-toluenesulfinate yields 3. Sulfone
3 is alkylated at its
α-sulfonyl position upon deprotonation with n-BuLi
followed by methyl iodide, ethyl, butyl, allyl,
and benzyl bromides, and 5-bromo-1-pentene, respectively.
Acylations occur using acid chlorides.
Dialkylation occurs upon further reaction with n-BuLi
and an alkyl halide. 1,4-Eliminations of
α,α-dialkyl sulfones 11 with tetrabutylammonium fluoride
(TBAF) give α,α-dialkyl-o-quinodimethanes (29); 3 is therefore a synthon for the
o-quinodimethane-α,α-dianion (34).
o-Quinodimethanes 29 undergo (1) cycloaddition with
acrylonitrile, acrylate esters, and alkyl
fumarates to yield 1,1-disubstituted-tetrahydronaphthalenes
(30) and (2) 1,5-sigmatropic rearrangements of hydrogen to give styrenes (32). The
stereochemistries of the various cycloadditions
reveal significant mechanism information.
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ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
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