Carbonyl alienation

Scheme 4.20. The formation of titanocene-vinylidenes and their application to carbonyl alienation.

Carbonyl alienation proceeds quite efficiently with titanocene alkenyUdene intermediate, formed in situ from alkenyltitanocene precursors. Indeed, these compounds are easily prepared from titanocene dichloride 65 and 2 equiv of alkenyl-magnesium bromide 66 followed by the addition of carbonyl derivatives 68 (Scheme 12.46) [66]. 

Vorteilhafter soil die Reduktion mit dem Trimethylammonium-Salz des Hydrido-tetra-carbonyl-eisen-Anions sein69. Das Reagenz ist leicht und billig herzustellen, jedoch muB in alien Fallen unter AusschluB von Feuchtigkeit und Sauerstoff gearbeitet werden ... 

Als Katalysator ist Palladium alien anderen tibergangsmetalien deutlich iiberlegen1 (vgl. Tab. 21) Raney-Nickel katalysiert Transferhydrierungen von Carbonyl-Verbindun-gen besser als andere heterogene Kontakte, wobei allerdings aromatische Ketone zu Me-thylen-Gruppen hydriert werden2 3. 

Alienation Another olefin metathesis-carbonyl olefination sequence utilizing titanacyclobutanes 11 is employed for the preparation of tri- or tetrasubstituted allenes [56]. Titanocene-methylidene 4 generated from 11 reacts with 1,1-disubsti-tuted allenes to produce the a-alkylidenetitanacyclobutanes 25 with the hberation of an olefin. Simple treatment of 25 with ketones and aldehydes at room temperature affords substituted allenes. The vinylidene complexes 26 are formed as the active species in these transformations (Scheme 4.20). 

Alienation of Carbonyl Compounds with Alkenyltitanocene Derivatives... 

Scheme 4.38. Alienation of carbonyl compounds with alkenyltitanocenes.

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