Ketones chlorotris rhodium

A number of metal complexes catalyze the hydrosilylation of various carbonyl compounds by triethylsilane. Stereoselectivity is observed in the hydrosilylation of ketones as in the reactions of 4-t-butylcyclohexanone and triethylsilane catalyzed by ruthenium, chromium, and rhodium metal complexes (eq 4). Triethylsilane and Chlorotris(triphenylphosphine)rho-dium(I) catalyst effect the regioselective 1,4-hydrosilylation of Q ,/3-unsaturated ketones and aldehydes. Reduction of mesityl oxide in this manner results in a 95% yield of product that consists of 1,4- and 1,2-hydrosilylation isomers in a 99 1 ratio (eq 5). This is an exact complement to the use of phenylsilane, where the ratio of respective isomers is reversed to 1 99. ... 

The synthesis of highly substituted /Sy-unsaturated ketones has been accomplished by reaction of allylmagnesium halides with 4,4-dimethyl-2-oxazolines. In the presence of a catalytic amount of chlorotris(triphenylphosphine)-rhodium(l), acyl chlorides and allyl tri-n-butyltin give the corresponding alkyl allyl ketone. A simple regiospecific synthesis of allyl ketones from allyl alcohols (Scheme 62) has been reported. ... 

In Section 4, it is described that chlorotris(triphenylphosphine)rhodium(I) (7) is quite an effective catalyst for the hydrosilylation of carbonyl compounds. For this reason, extensive studies on asymmetric hydrosilylation of prochiral ketones to date have been based on employing rhodium(I) complexes with chiral phosphine ligands. The catalysts all prepared in situ are rhodium(I) complexes of the type, (BMPP>2Rh(S)a (8) [40] and (DIOP)Rh(S)Cl (6) [41], and a cationic rhodium(III) complex, [(BMPP)2lUiH2(S)2] Q04 (5) [42], where S represents a solvent molecule. An interesting polymer-supported rhodium complex (V) [41], and several chiral ferrocenylphosphines [43], recently developed as chiral ligands, have also been employed for asymmetric hydrosilylation of ketones. Included in this section also are selective asymmetric hydrosilylation of a,0-unsaturated carbonyl compounds and of certain keto esters. 

Since the intermediacy of a-siloxyalkyl rhodium complex III (see Scheme 4) is strongly suggested in the hydrosilylation of terpene ketones catalyzed by chlorotris-(triphenylphosphine)rhodium(I) (7), such an intermediate most likely plays a key role in the asymmetric induction of the present system. The fundamental premise is to assume a square-pyramidal structure of the a-siloxyalkyl-rhodium intermediate VI, as shown in equation (18), on the basis of the established structures of dihydrido [46] and of silylhydrido [14, 32c, 47] complexes derived from the Wilkinson s rhodium(I) complex. 

Substituted v-butyrolactones can be prepared by reaction of aldehydes or ketones with tbe dianion (28), and direct condensation of symmetrical ketones with diethyl 2-oxomalonate provides a useful synthetic route to the butenolides (29). A number of initiators have been used previously to promote the free-radical addition of ketones to alkenes now transition-metal oxides have been shown to be effective. Pent-4-enal is cyclized to cyclopentanone by chlorotris(triphenylphos-phine)rhodium(i) through a non-radical pathway. ... 

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