Phosphoramidite Taddol-based

Phosphoramidite ligands based on TADDOL (36) and on D-mannitol (37) [74] have also been used (Scheme 28.11). However, the enantioselectivities reported for the hydrogenation of a-dehydroamino acids and itaconates were generally lower compared to the ligands based on BINOL. A different strategy is the use of ligands 38a-g based on the achiral diol catechol, and chiral amines [75]. 

Scheme 7.13. TADDOL-based phosphoramidite ligands in the catalytic 1,4-addition.

Alexakis, employing various chiral trivalent phosphorus ligands, has recently described Cu(OTf)2-catalyzed 1,4-additions of Et2Zn to a number of nitroalkenes (Scheme 7.22) [77]. TADDOL-based phosphonite 82 gave the highest ees for ar-ylnitroalkenes (up to 86%), whereas phosphoramidite 18 is the ligand of choice for alkylnitroalkenes [ees of up to 94%). 

Alkylidenemalonate 59 was a substrate in the Taddol-based phosphoramidite 61-mediated addition of diethyl zinc to afford the ethyl adduct 60 in 73% ee [39]. The unsaturated imine 62 was a substrate in an amidephosphine 64 copper-catalyzed ethylation to afford 63 in moderate ee after hydrolysis (Scheme 7) [40]. 

You, this work employed the iodo substrates which allowed the cleavage of a weaker C—I bond. Different planar chiral metallocenes can be synthesized in good to excellent yields and high enantioselectivity with good functional group tolerance. Very recently Gu and co-workers successfully extended this strategy to access planar chiral quinilinoferrocenes, but the enantioselectivity was only moderate (Scheme 5.29c). Almost at the same time, Liu, Zhao, and co-workers found that the use of the TADDOL-based phosphoramidite... 

A lower range of ee-values was obtained using chiral carbene ligand 17 [15], iPr-DuPHOS (18) [16] and diethyleneamine-bridged phosphoramidite 19 [17]. To date, the best enantioselectivities using this protocol were achieved with Kondo s hemilabile TADDOL-based phosphine-phosphine oxide 20 [18] and Zhou s spirocyclic phosphite 21 (Figure 8.3) [19]. 

Cramer reported the synthesis of TADDOL-based phosphoramidites 55, which were compared with other already known TADDOL-type phosphoramidites already evaluated in palladium(0)-catalysed asymmetric C-H functionalizations, used for the synthesis of valuable p-lactams. The evaluation of the different TADDOL phosphoramidites revealed that the... 

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