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4.1.2.2.2 With Water-Insoluble Catalysts

DOI: 10.1055/sos-SD-206-20216

Wu, X.; Xiao, J.Science of Synthesis: Water in Organic Synthesis, (20121291.

Although the water-soluble catalysts with ligands 29 are effective for the asymmetric transfer hydrogenation of dihydroisoquinoline-type substrates, a simpler method involves the use of the Noyori catalyst 41 in the presence of a surfactant or of silver(I) hexafluoroantimonate. A range of 3,4-dihydroisoquinolines and related cyclic imines can be reduced with sodium formate in water, affording excellent enantioselectivities in most cases (Table 3).[‌194‌] However, a large quantity of hexadecyltrimethylammonium bromide (100mol%) is generally required. Polycyclic iminium salts can be reduced under similar reduction conditions, but require the addition of silver(I)hexafluoroantimonate, which presumably helps to generate a cationic ruthenium(II) catalyst. The protocol permits ready access to the indoloquinolizidine alkaloid ()-(S)-harmicine (101) and its homologue 102. In addition, imine substrates with aryl substituents conjugated to the imino bond can also be reduced. A Lewis acid is added in this case, which activates the imine toward hydride attack. In general, these imines are more difficult to reduce.

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8.8 M8M, 88°M 88 88 88.8 [‌888‌]
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8.8 M8M, 88°M 88 88 >88 [‌888‌]
8.8 MeMeM8 (8eee%), M8M, 88°M 88 88e 88 [‌888‌]
8.8 MeMeM8 (8eee%), M8M, 88°M 88 88e 88 [‌888‌]
8.8 MeMeM8 (8eee%), M8M, 88°M 88 88 88 [‌888‌]
8.8 MeMeM8 (8eee%), M8M, 88°M 88 88 88 [‌888‌]
8.8 MeMeM8 (8.8eee%), Me(MMe)8 (88eee%), M8M, 88°M 88 88e 88 [‌888‌]
8.8 MeMeM8 (8.8eee%), M8M, 88°M 88 88 88 [‌888‌]
8.8 MeMeM8 (8.8eee%), Me(MMe)8 (88eee%), M8M/MeMM (8:8), 88°M 88 88 88 [‌888‌]
8.8 MeMeM8 (8.8eee%), Me(MMe)8 (88eee%), M8M/MeMM (8:8), 88°M 88 88e 88 [‌888‌]
8.8 MeMeM8 (8.8eee%), Me(MMe)8 (88eee%), M8M/MeMM (8:8), 88°M 88 88 88 [‌888‌]

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M8 M8 M8 Meeeeeee Meee (e) Meeee (%) ee (%) Mee
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Me M M 888 8 88 88 [‌888‌]
Me M M 888 8 88 88 [‌888‌]
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8-MM8M8 M M 888 88 88 88 [‌888‌]
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Meeeeeeeeee 88

M8 M8 ee Meeee (%) ee (%) Mee
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References