Hydrogenation of allylic alcohols

Diasterocontrolled hydrogenation of allylic alcohols directed by the -OH group... 

The development of Ir-chiral N,P ligand system opens another promising way for the hydrogenation of allylic alcohol and its derivatives. For example, a cationic Phox-Ir complex catalyzes the hydrogenation of ( )-2-methyl-3-phenyl-9-propen-l-ol in a highly enantioselective fashion.178 With 1 mol.% (5)-92-Ir catalyst, the hydrogenation proceeds completely to provide the chiral alcohol product in 96% ee. Under the same conditions, a para- Bu-substituted chiral alcohol derivative is obtained with 94% ee for the synthesis of lilial (Equation (59)). Heterocyclic N, P-ligand, HetPHOX 113, is also efficient for this reaction.191... 

Mechanistic study revealed that the reaction proceeds through intramolecular 1,3-hydrogen migration, and the chiral rhodium catalyst differentiates the enantiotopic C-l hydrogens of allylic alcohols (Scheme 29).53... 

The team of Crooks is involved in the synthesis and the use of dendrimers and, more particularly, poly(amidoamine) dendrimers (PAMAM), for the preparation of dendrimer-encapsulated mono- or bimetallic nanoparticles of various metals (Pt, Pd, Cu, Au, Ag, Ni, etc.) [55, 56]. The dendrimers were used as nanocatalysts for the hydrogenation of allyl alcohol and N-isopropylacrylamide or other alkenes under different reaction conditions (water, organic solvents, biphasic fluorous/or-ganic solvents or supercritical COz). The hydrogenation reaction rate is dependent on dendrimer generation, as higher-generation dendrimers are more sterically... 

Entries 8-13 in Table 21.9 illustrate the effect of S-O coordination on the hydrogenation of allyl alcohols. The hydrogenation of (a-hydroxyalkyl)vinyl sul-fones follows the same stereochemical course as the corresponding acrylate via HO coordination (entries 8 and 9). However, the hydrogenation of (a-hydro-xyalkyl)vinyl sulfoxides is directed by S-O coordination, which overrides the HO-participation in the stereochemical course (entries 10-13) [56]. The directing power of S-O may be limited to vinylic examples, as compounds having the S-O and double bond in an allylic relationship failed to reduce under the standard conditions. 

The hydrogenation of allylic alcohols and a,/>-unsaluraled acids leads to products with a very high synthetic potential, and both transformations were used quite early for industrial applications. In both cases Ru complexes with axially chiral biaryl ligands (binap analogues) are the catalysts of choice. Here, we will dis-... 

For hydrogenation to take place, the substrate usually needs to bind to the metal complex, although exceptions are known to this rule [25]. Substrate inhibition can occur in a number of ways, for example if more than one molecule of substrate binds to the metal complex. At low concentration this may be a minor species, whereas at high substrate concentration this may be the only species. One example of this is the hydrogenation of allyl alcohol using Wilkinson s catalyst. Here, the rate dependence on the substrate concentration went through a maximum at 1.2 mmol IT1. The authors propose that this is caused by formation of a complex containing two molecules of allyl alcohol (Scheme 44.1) [26],... 

Scheme 44.1 Substrate inhibition in the hydrogenation of allyl alcohol.

ASYMMETRIC HYDROGENATION OF ALLYLIC ALCOHOLS USING BINAP-RUTHENIUM COMPLEXES (S)-(-)-CITRONELLOL (6-Octen-1-ol, 3,7-dimethyl, (S)-)... 

Fig. 19. Turn-over frequencies for hydrogenation of allyl alcohol and N-isopropyl acrylamide obtained in water using dendrimer-encapsulated Pd nanoparticles of constant average size. The hydroxyl-terminated PAMAM dendrimer generation varies from G4 to G8...

Toluene solutions of Pd encapsulated within dendrimer-templated inverted micelles have been tested for catalytic activity by examining their effectiveness towards hydrogenation of allyl alcohol in organic solvents [19]. The reaction product was confirmed to be n-propanol by H NMR spectroscopy, and the turnover frequency, calculated from the rate of hydrogen uptake, was 760 mol H2 (mol Pd) h at 20 °C. This value compares favorably with the value of 218 mol H2 (mol Pd) h obtained for the same reaction carried out in water using Pd nanoparticles encapsulated in hydroxy-terminated dendrimers. 

SCH EME 29. Asymmetric hydrogenation of allylic alcohols catalyzed by Ru(OCOCH3)2-[(S)-binap] in methanol at 4 and 100 atm. 

The iridium catalyst [lr(COD)py(PCy )PFA] is utilized in substrate-controlled hydrogenations of allylic alcohols of the type 34, 36, and 38.25 The catalyst coordinates with the hydroxy group in the molecule, so hydrogenation occurs on ) from one side. 

A cationic Ir complex possessing phosphanodihydrooxazole 26 is usable for asymmetric hydrogenation of allylic alcohols. (E)-2-Methyl-3-phenyl-2-propen-l-ol can be converted in CH2C12 containing 1 mol % of the Ir complex to the saturated product in 95% yield and 96% ee (Scheme 1.26) [141]. The process is used in the enantioselective synthesis of the artificial fragrance filial. 

Asymmetric hydrogenation of allylic alcohols (14, 38-40).4 Full details are ivailable for the preparation of Ru(OAc)2[(R)- or (S)-BINAP], the catalyst for asym-... 

Ruthenium and rhodium complexes that contain TMBTP have shown utility in the asymmetric hydrogenation of allylic alcohols,155,156 P-keto esters,155,157 and a,P-unsaturated carboxylic acids.155... 

The decahydroisoquinoline derivative NVP-ACQ090 (124) is a potent and selective antagonist at the somatostatin sst3 receptor. The asymmetric hydrogenation of allylic alcohol 125 with a rhodium catalyst that contained (S)-TMBTP produced (A )-126 (97.5% ee) (Scheme 12.50). The authors indicated that enantiomerically pure 124 could be obtained from material acquired by asymmetric hydrogenation and that the process is suitable for large-scale production.156... 

Fig. 6 Turnover frequencies (TOFs) for the hydrogenation of allyl alcohol using G6-Qii6(Pd55+K) and G6 Qi is[Au55 ](F d ), which was prepared using the sequential-loading method, for n = 0, 95, 255, 455. Conditions 22 °C, substrate metal = 3300 1, [Pd +Au] = 150 xM. The represent TOF data for Pd-only DECs, while the o represent data for the bimetallic DECs. Reprinted with permission from J Am Chem Soc, 2004, 126, 15583-15591. Copyright 2004 American Chemical Society...

Asymmetric hydrogenation of allylic alcohols (14, 39-40).1 Mammalian dol-ichols (2) are terminal dihydropolyisoprenols which are involved in glycoprotein synthesis. They contain one terminal chiral primary allylic alcohol group. The polyprenols 3 present in plants correspond to dolichols except that they lack the terminal double bond considered to be (Z). They can be obtained by hydrogenation of 2 catalyzed by (bistrifluoroacetate)ruthenium(II) and (S)-l, which affects only the terminal double bond to provide (S)-3 in >95% ee. 

BINAP-ruthenium(II) is particularly good at catalysing the hydrogenation of allylic alcohols, and of a,(3-umaturated carboxylic adds to give acids bearing a stereogenic centres (like naproxen above). 

Figure 8. A phosphane modified PEO-PPO-PEO block copolymer as thermoresponsive catalyst in the hydrogenation of allylic alcohols.

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