Carbonyls methylenation

Elaborate organic substrates and dicarbonyl compounds can also be methylenated in high yields with the Tebbe reagent (Table 3.8) [699-702]. Acid chlorides or 

Most experimental data suggest that the actual methylenating agent derived from the Tebbe reagent upon treatment with a weak base, is the highly reactive carbene complex Cp2Ti=CH2 [709]. This complex is a typical Schrock-type carbene, because it is high-valent [Ti(IV)], electron-deficient (16 valence electrons) and nucleophilic at carbon. 

/ Ti Al Tebbe reagent methylenation of aldehydes, ketones, esters, thioesters, amides, carbonates can also induce olefin metathesis in situ preparation [711-713] 

CpjZrClj, Zn, CHjBrj, THF methylenation of aldehydes, ketones no reaction with esters [714] 

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Formation of cyclic enol ethers by carbonyl methylenation—olefin metathesis. 

Table 14.5. Carbonyl methylenation utilizing titanocene-methylidene...

The reaction of 1,3-dithietane 92f substituted with a diethylphosphoryl group with G-nucleophiles is analogous to the previously reported reaction. Its condensation with different C-nucleophiles, such as cyclic and acyclic a-carbonyl-methylenes and a-carbonylhydrazones, gave a number of [2,l-3]fused phosphono-substituted thioxopyranes 97, 100, 103, 107, oxadiazine 109, and thiazine 105 (Scheme 12), which are of potential biological interest <2002PS1885>. 

Irradiating at rather short wavelengths (approx. 300 nm) is essential for realizing the unique regioselectivity. When short wavelengths (below 325 nm) were cut off, the weakest C-H bonds were carbonylated methylene in alkanes and benzylic methyl in toluene (Scheme 7). 

Carbonyl Methylenation and Alkylidenation Using Titanium-Based Reagents... 

Scheme 3. Carbonyl methylenation with the titanium-methylene species 4 prepared from the Tebbe, Grubbs, or Petasis reagents (1 - 3).

Carbonyl methylenation The reagent reacts with carbonyl compounds to form, after hydrolysis, 2-triphenylstannylethanols (2), which form olefins (3) on pyrolysis at 110-175°. Overall yields are improved if the alcohols (2) are not isolated. Examples ... 

Acylamino-thiocarbonyl)-alkoxy-carbonyl-methylen]- -bis-[cyclohexylamid] E15/2, 2176 (H CS-NH-CO-R)... 

Propansaure 3-(2,5-Dichlor-phenylsulfonyl)- VI/2, 550 Thiophen 2,5-Dichlor-l-(dimethoxy-carbonyl-methylen)- Ell, 1369 [N2C(COOR)2 + Het]... 

Hydroxylamin N-(Cyan-ethoxy-carbonyl-methylen)-0-(4-nitro-benzoyl)- E5, 780 (OH - O-CO-Ar)... 

Hydrazin 1,2-Diethoxycarbonyl-l-(2,4-dihydroxy-phenyl)- X/2, 289 Imidazolidin l-Butyl-2-(dimethoxy-carbonyl-methylen)-4,5-dioxo-E15/2, 2238 [En— 1,1-diamin + ROOC-COOR]... 

Pine, S. H. Carbonyl methylenation and alkylidenation using titanium-based reagents. Crg. React. 1993,43, 1-91. 

Treatment of 2-bromoacetylthiazole (142) with tripenylphosphine affords the phosphonium salt which on treatment with aqueous sodium hydroxyde gives the stabilized [(2-thiazolyl-carbonyl)methylene]triphenylphosphorane (143) (Scheme 35) <9lTL3247, 94ja3324>. This compound... 

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