Tebbe reaction

The Tebbe reaction, which converts the oxo groups of esters and lactones to methylene groups to give enol ethers, is described in section 2.1.2. 

Application of the Emend Process (Tebbe Reaction followed by hydrogenation)... 

Examples have also been reported in which glyconolactones are olelinated generating exoenitols (Fig. 10) for example by methylenation (Tebbe reaction),20 difluoromethylenation,21 and dichloromethylenation,22 the Wittig olefination.23... 

Tebbe reaction 148 Tetracyclin synthesis 190 Tetrazole synthesis 17 Tetrodotoxin synthesis 136 Tocopherol synthesis 142 Tonantzitlolone synthesis 188 Triazine synthesis 17 Triclavulone synthesis 102... 

Dormond ef rrZ. have exploited compounds 30 and particularly 32 as synthetically useful reagents. The uranium-mediated methylenation of carbonyl compounds (cf.. the Wittig, Peterson or Tebbe reactions) is illustrated in Equation (5.1). The instantaneous formation under ambient conditions of the insertion product 33 was essentially quantitative (e.g./ =... 

In the Tebbe reaction with pyridine iV-oxides and their benzo derivatives, regioselective attack at the cr-position occurs along with the expected deoxygenation (Equations 47 and 48) <2000AGE2529>. The presumed organome-tallic intermediate is the titanocene methylidene complex [Cp2Ti=CH2]. 

Sn2 substitution, 225 StilL-Wittig rearrangement, 227 Tebbe reaction, 231 types, 208... 

Tebbe reaction, 231 Tetrabutylanunonium azide, 133 Tetramethylurea (TMU), 436 2-Thiopyridylcaibonate (TOPCAT) glycosyl donors, 431 preparation, 434, 440 design, 432 reactivity, 435... 

The methylenation of ketones and aldehydes by the Wittig reaction is a well-established and selective methodology. Unlike addition-elimination methods of alkene formation, the Wittig proceeds in a defined sense, producing an alkene at the original site of the carbonyl. The Wittig reaction is not considered here, but is used as the standard by which the methods discussed are measured. The topics covered in the methylenation sections include the Peterson alkenation, the Johnson sulfoximine approach, the Tebbe reaction and the Oshima-Takai titanium-dihalomethane method. 

A reaction that appears to be mechanistically similar to the Tebbe reaction was developed by Oshima in 1978. Diiodomethane or dibromomethane in the presence of zinc is treated with a Lewis acid to form, presumably, a divalent complex (72), which reacts with aldehydes and ketones to produce the corresponding methylene derivative (73 Scheme 18). This reagent complements the reactivity of the Tebbe reagent, in that the zinc methylenation is not reactive towards esters or lactones. Because it is an electrophilic reagent, it is suitable for the methylenation of enolizable ketones and aldehydes. 

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