Diaminophosphine oxide ligands

Cramer and co-workers reported a Ni-catalyzed asymmetric hydrocarbam-oylation reaction of alkenes with diaminophosphine oxide ligands. The acyl C—H bond of a carbamate group was directly functionalized. It is known that secondary phosphine oxides are usually air-stable and robust preligands because of their unique tautomerization between P and In the presence of bases or transition metals, such an equilibrium can be shifted to the trivalent phosphinous acid and thus provide the opportunity for hetero-bi-metallic catalysis where a late transition metal and an early transition metal can coordinate to the phosphorus atom and the oxygen atom, respectively (Scheme 8.17). 

Bearing this idea in mind, the authors synthesized a class of chiral diaminophosphine oxide ligands and tested them in the Ni-catalyzed intramolecular asymmetric hydrocarbamoylation reactions of formamides 38 with AlMCa as the other metal catalyst (Scheme 8.18). The combination of [Ni(cod)2] and (i ,i )-L3 gave the optimal catalytic activity. Substrates with various substitution patterns were converted smoothly to their corresponding pyrrolidinones 39 in up to 98% yield and 95% ee under very mild conditions. 

Donets and Cramer have developed an asymmetric version of these hydrocar-bamoylation reactions using a diaminophosphine oxide ligand (Scheme 5.40, Table 5.11).44... 

The phosphoramidite ligands that are the focus of the remainder of this chapter have prompted the investigation of ligands containing related structures. Iridium complexes of aspartic acid-derived P-chirogenic diaminophosphine oxides (DlAPHOXs) catalyze the amination [62] and alkylation [63] of aUyhc carbonates (Scheme 6). With BSA as base and catalytic amounts of NaPFs as additive, branched amination and alkylation products were obtained from cinnamyl carbonates in excellent yields and enantioselectivities. However, the yields and enantios-electivities were lower for the reactions of alkyl-substituted aUyhc carbonates. Added LiOAc increased the enantioselectivities of aUyhc alkylation products. 

Nemoto and Hamada [50] has described the development of a new class of chiral phosphorus ligand - aspartic acid-derived P-chirogenic diaminophosphine oxides, DIAPHOXs - and their application to several Pd-catalyzed asymmetric allylic substitution reactions. Pd-catalyzed asymmetric allylic alkylation was initially examined in detail using diaminophosphine oxides 77, resulting in the highly enantioselective construction of quaternary stereocenters. With the use of the Pd-DIAPHOX catalyst system, asymmetric allylic alkylation, asymmetric allylic amination, and enantioselective construction of quaternary carbons were achieved with high ee (up to 97-99% in many cases) (Scheme 24). 

The new complex (166), generated from the corresponding diaminophosphine oxide and Mc3 Al, has been employed as a chiral ligand for the Ni(0)-catalysed C-H activation of A-homoallyl formamide (163), which provides pyrrolidones (165) via intramolecular hydrocarbamoylation (164) in <94%... 

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