Catalyst phospholane

Scheme 24.7 Non-standard a-dehydroamino acid derivatives reduced by Rh-phospholane-based catalysts.

Fig. 24.8) [122]. Whilst this protocol can be used to prepare 3-pyridyl-alanine derivatives [22], the corresponding 2-pyridyl-alanine cannot be made [122]. However, Adamczyk has prepared several 2-pyridyl-alanine analogues through hydrogenation of the pyridine-N-oxide substrates in 80-83% ee (see Fig. 24.8) [123]. In general, only when the 2- and 6-positions of the pyridine ring are occupied can 2-, 3- or 4-pyridyl-alanine derivatives be prepared, without nitrogen modification, via hydrogenation with [phospholane-Rh]+ catalysts [122-124].

Table 24.2 Phospholanes reported to hydrogenate model jS-dehydroamino acid derivatives in >95% ee. AcHN C02R2 Rh-catalyst AcHN C02R2...

Fig. 24.11 Unusual /t-dehydroamino acid derivatives to have been reduced with phospholane-based catalysts.

Table 24.4 Phospholanes reported to hydrogenate model itaconic acid substrates in >95% ee. Rh-catalyst...

Fig. 24.15 Diverse a,jS-unsaturated acid derivatives reduced with phospholane catalysts.

Through continued exploration of the applicability of enantiomeric hydrogenation, phospholane-based catalysts have been reported to be efficient for the reduction of several atypical olefinic substrates (Fig. 24.18). 

ThrePHOX complexes. The phospholane 54 and catalyst 57, however, gave promising results for the hydrogenation of a,/J-uri saturated carboxylic esters. 

Carbohydrates remain an attractive source of chirality in preparation of ligands for asymmetric catalysis. Functionalized phospholanes, 192 [167], and chiral bisphosphinites 193 [168] with an attached crown ether unit were obtained recently from D-mannitol and from phenyl 2,3-di-0-allyl-4,6-0-benzylidene-p-D-glucopyranoside, respectively (Figure 18). Compounds 194 and 195 were obtained in the photochemical addition of H2P(CH2)3PPH2 onto the crresponding alkenes - Pd-complexes of these new bisphosphines were successfully applied as catalysts in the copolymerization of CO and... 

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