Easier Preparation of 2,6-Di-tert-butylphenyl Derivatives ^¹

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*-CO₂H (63%). The corresponding 4-methyl-derivatives of these compounds were obtained analogously. The acid chloride xyl*-COCl (77% yield) acylates HalMgCH₂R 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

References

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1

Sterically Congested Molecules, Part 21. Part 20 is ref. 23.

6

Schemes 20 and 23 in ref. 14.

25

This supports the E-configuration.