Abstract
Despite steric shielding by the 2,6-di-tert -butylphenyl group
(‘super-2,6-xylyl’ = xyl*),
inexpensive sodium phenolate (xyl*-ONa) reacts
with dimethyl sulfate to produce only xyl*-OCH3 (94%)
with complete suppression of the alternative 4-methylation. Reductive
cleavage of xyl*-OCH3 by elemental
lithium with the help of an electron carrier generates xyl*-Li,
which in turn yields xyl*-CO2 H (63%).
The corresponding 4-methyl-derivatives of these compounds were obtained
analogously. The acid chloride xyl*-COCl (77% yield)
acylates HalMgCH2 R to give only xyl*-COCH3 (86%)
or xyl*-COEt (97%). These two ketones
react with n -butyllithium (no carbonyl
addition) and Cl-PO(OEt)2 to furnish only the
enol phosphates xyl*-C(=CH2 )OPO(OEt)2 (84%)
or xyl*-C(=CHCH3 )OPO(OEt)2 (up
to 70%), respectively. Only 1,2-elimination occurs when
the latter two products are treated with tert -butyllithium,
affording xyl*-C≡CH (68%) or
xyl*-C≡CMe (88%), respectively.
Key words
acylation - alkynes - deoxygenation - electron
transfer - ketones
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