Directing groups catalyst-controlled

Catalyst-Controlled Directing Groups in Cross-Dehydrogenative Coupling 181... 

Scheme 3. Design of a catalyst-directing group for the control of diastereoselectivity upon hydroformylation of acyclic methallylic alcohols.

Support for the role of the o-DPPB substituent as a catalyst-directing group was provided in a control experiment with the benzoate 7. Thus, exchanging the phosphorus of the o-DPPB group with a CH moiety, itself not able to coordinate to the catalytically active rhodium center, caused a complete loss of stereoselectivity in the hydroformylation reaction [10]. 

Interestingly, the same concept involving a catalyst-directing group allowed also to make efficient use of 1,3 asymmetric induction. This, of course, is a much more difficult situation, since additional degrees of freedom have to be controlled in the course of the stereo-... 

Tin(IV)-chloride-mediated double aldol reaction of acyclic ketones is rendered stereoselective by a chiral phosphine oxide, (5)-BE JAPO it is proposed that the catalyst controls the first aldol and the substrate controls the second. Another chiral diphosphine oxide, this one based on thiophene, catalyses direct aldols in high delee Chiral a-silyloxy ketones derived from lactate (61) undergo titanium(IV)-mediated aldols giving diastereomerically pure syn-syn adducts (62) in high yield, irrespective of the alkyl groups fianking the silyl or carbonyl. 

Abstract Iron-catalyzed C-H bond activation followed by C-C bond formation has received much attention in recent years, motivated by the environmental and economical merits of iron, as well as the scientific challenge in controlling and understanding the reactivity of iron species. This review describes the utilization of iron as a catalyst for directed C-H bond activation, followed by C-C bond formation. Catalytic activation of C(sp )-H and C(sp -H) bonds, followed by oxidative reaction with nucleophiles, or reaction with electrophiles is described. Reactions of substrates possessing a directing group are mainly discussed, but other substrates are also presented. Carbon-heteroatom bmid formation is also briefly discussed. 

Cobalt NHC catalysts have been reported to promote intramolecular olefin hydroary-lation of Ai-homoallyl indoles (158), having a C(3) aldimine directing group, to afford the 5-mco-trig (159) and 6-enr/o-trig (160) products. The course can be controlled by the choice of the NHC ligand. 

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