Reactivity of the uranium-carbon σ-bond in ‘silylamido’ compounds

Abstract

The uranium-methyl σ-bond of (N(SiMe 3) 2) 3UCH 3 ( 1)and the uranium-methylene σ-bond of the metallacycle (N(SiMe 3) 2) 2 UCH 2SiMe 2N SiMe 3 ( 2) are very reactive towards insertion reactions and nucleophilic substitution reactions. Their reactivity can be used in organic synthesis. Compounds 1 and 2 reacted readily with isocyanides, nitriles and carbonyl compounds R 1R 2CO. Aldehydes, ketones and esters inserted rapidly in compound 2, affording quantitatively the six-membered metallacycles: (N(SiMe 3) 2) 2UOC(R 1R 2)CH 2SiMe 2NSiMe 3. These metallacycles were hydrolyzed leading to methylketones (from esters) and to vinyl compounds (from aldehydes and ketones) in high yields. The insertion reaction was highly stereoselective. Compound 2 is a very rapid, clean and high yielding methylenation reagent. It can be used instead of ‘Tebbe's reagent’ to synthesize vinyl compounds from carbonyls. 1 reacted rapidly with aldehydes, much more slowly with aliphatic, cyclic and aromatic ketones, but did not react with sterically hindered ketones or esters. Hydrolysis of the intermediate alkoxy- uranium (N(SiMe 3) 2) 3UOCR 1R 2CH 3 gave the corresponding secondary or tertiary alcohols. Compound 1 is a very highly chemoselective reagent of methylation of aldehydes versus ketones and a highly stereoselective reagent.