Lithium (3,3-Dimethyl-1-butynyl)methylcuprate

[41602-02-2]  · C7H12CuLi  · Lithium (3,3-Dimethyl-1-butynyl)methylcuprate  · (MW 166.68)

(mixed cuprate methyl transfer agent)

Alternate Name: lithium (t-butylethynyl)methylcuprate

Preparative Methods: by the addition of Methyllithium to 3,3-Dimethyl-1-butynylcopper(I) at -40 °C in ether or THF.1

Handling, Storage, and Precautions: air- and moisture-sensitive. Use in a fume hood.

Methylating Agent.

House and Umen demonstrated that lithium (3,3-dimethyl-1-butynyl)methylcuprate (1) would transfer a methyl group to the relatively unreactive isophorone (2) in 76% yield with a 12% recovery of starting material.1 The reaction rate was significantly slower than the rate of methyl transfer from the homocuprate Lithium Dimethylcuprate to (2). While Me2CuLi reacted slowly with enone (4), there was no reaction with mixed cuprate (1) (eqs 1 and 2).

A study designed to evaluate the electron transfer abilities of several organocuprates showed that mixed cuprate (1) effectively converts keto-mesylate (5) into cyclopropyl ketone (6). Reaction of (1) with (5) at -78 °C in THF produced a 50% yield of (6), and at 0 °C the yield of (6) improved to 95% (eq 3).2

Related Reagents.

3,3-Dimethyl-1-butynylcopper(I); Lithium (3,3-Dimethyl-1-butynyl)vinylcuprate; Lithium Dimethylcuprate.

1. House, H. O.; Umen, M. J. JOC 1973, 38, 3893.
2. Hannah, D. J.; Smith, R. A. J.; Teoh, I.; Weavers, R. T. AJC 1981, 34, 181.

Matthew E. Voss

The Du Pont Merck Pharmaceutical Company, Wilmington, DE, USA

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