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Synfacts 2024; 20(04): 0391
DOI: 10.1055/s-0043-1773176
Metals in Synthesis

The Takai–Oshima–Lombardo Methylenation of Carbonyl Compounds

Contributor(s):
Martin Oestreich
,
Hendrik F. T. Klare
,
Aliyaah J. M. Rahman
Takai K, Hotta Y, Oshima K, *, Nozaki H. Kyoto University, Japan
Effective Methods of Carbonyl Methylenation using CH2I2–Zn–Me3Al and CH2Br2–Zn–TiCl4 System.

Tetrahedron Lett. 1978;
27: 2417-2420
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Lombardo L. * Australian National University, Canberra, Australia
Methylenation of Carbonyl Compounds with Zn-CH2Br2-TiCl4. Application to Gibberellins.

Tetrahedron Lett. 1982;
23: 4293-4296
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Key words

carbonyl compounds - methylenation - olefination - titanium - zinc

Significance

The Takai–Oshima–Lombardo methylenation is a synthetically important reaction to convert carbonyl compounds into alkenes. Initially introduced by Takai, Oshima and co-workers in 1978, this transformation was further elaborated by Lombardo in 1982. The Zn/CH2Br2/TiCl4 system is also known as the Lombardo–Oshima reagent.


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Comment

The highly electrophilic methylenation reagent is formed in situ and stable at low ­temperatures. In contrast to the Wittig reaction, this protocol is applicable to base-sensitive substrates, as demonstrated by the olefination of ­enolizable gibberellin derivatives without erosion of enantiomeric excess. The structure of the active species is assumed to be a gem-dimetallic species (see path a).


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Publication History

Article published online:
13 March 2024

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