Chiral Hetero‐ and Carbocyclic Compounds from the Asymmetric Hydrogenation of Cyclic Alkenes

Abstract

Several types of chiral hetero-and carbocyclic compounds have been synthesized using the asymmetric hydrogenation of cyclic alkenes. N, P-ligated iridium catalysts reduced six-membered cyclic alkenes with various substituents and heterofunctionality in good to excellent enantioselectivity; whereas the reduction of five-membered cyclic alkenes was generally less selective, giving modest enantiomeric excesses. The stereoselectivity of hydrogenation depended more strongly on substrate structure for the five-rather than sixmembered cyclic alkenes. The major enantiomer formed in the reduction of six-membered alkenes could be predicted from a selectivity model and isomeric alkenes had complementary enantioselectivity, giving opposite optical isomers upon hydrogenation.The utility of the reaction was demonstrated by using it as a key step in the preparation of chiral 1,3-ciscyclohexane carboxylates.

Asymmetric Hydrogenation of Olefins Using Chiral Crabtree-type Catalysts: Scope and Limitations

“…Unfortunately, the reduction of such alkenes has been shown to proceed only slowly. 153 Five-membered methyl-and phenylsubstituted alkenes S186 and S187 were reduced in good enantioselectivity but only to 20% conversion after 24h under 100 bar H 2 using catalysts based on bicyclic ligands 17b (Figure 4) and 49b ( Figure 6) (Scheme 29). For the six-membered variants, phosphine-imidazole ligand 41b ( Figure 6) gave similar selectivity and conversion for the phenyl-derivative S188 while the methyl-substituted alkene S189 was completely reduced.…”

Minor secoiridoid aglycones from the low-polarity part of the traditional Chinese herb: Swertia mileensis

“…The configuration at C-9 was determined as R-form based on its optical rotation ([α] 18 D -12.4) and in comparison to the known compounds with the similar chiral center. 18,19 Thus, the structure of compound 1 was determined and named as swerimilegenin A.…”

Thiazole, Imidazole and Oxazoline Based N,P‐Ligands for Palladium‐Catalyzed Cycloisomerization of 1,6‐Enynes

“…The substrates 1 , 9 , 10 , 11 , 13 , 14 , 15 , 18 were prepared according to the reported procedure. The N,P‐ligands L1 , L2 , L4 , L5 ,, L6 , L7 , L8 were prepared according to the reported procedure. All reagents were used as supplied commercially without further purification.…”