Intramolecular ene reactions catalyzed by NbCl5, TaCl5 and InCl3

Abstract

Niobium pentachloride, tantalum pentachloride and indium trichloride efficiently catalysed the cyclization of (R)-citronellal to a mixture of isopulegol and neoisopulegol in good yields. A comparative study was carried out which demonstrated that NbCl 5 is the most active Lewis acid whereas InCl 3 is the most selective one. The selectivity of the reactions varied according to the Lewis acid used and to the solvent. The ene reaction of a 1,7-diene was also investigated. In this case, all Lewis acids tested showed excellent selectivity.

Lewis acid catalysis and Green oxidations: sequential tandem oxidation processes induced by Mn-hyperaccumulating plants

“…The selectivity toward the isomer of interest, (−)isopulegol, is higher with Eco-Mn 1 than those obtained with others transition metal chlorides such as: ZnCl 2 , FeCl 3 , TiCl 4 , SnCl 4 , SbCl 3 (Nakatani and Kawashima 1978) InCl 3 , NbCl 5 , TaCl 5 (Andrade et al 2004), and CuCl 2 (Alaerts et al 2006).…”

Enantiomeric Isopulegol as the Chiral Pool in the Total Synthesis of Bioactive Agents

“…A wide range of Lewis acid and Brønsted catalysts such as InCl 3 , [19] ZnBr 2 , [20] ZnBr 2 /SiO 2 , [21] ZnCl 2 /SiO 2 , [22] Al 2 O 3 / SiO 2 , [23] ZnBr 2 /C 8 -HMS, [24] Zr-beta-100, [25] SÀ ZrO 2 -CMS (carbon molecular sieve), [26] ZrO 2 À 16-PO 4 -500, [27] Zr-TUD-1, [28] H-MCM-41, [15] Al/Fe-pillared Clay (Al/Fe/PILC), [29] BINOLÀ Al, [30] H 3 PW 12 O 40 /SiO 2 , [13] HfO 2 (SiO 2 ) 8 , [31] TBA 3 H-[γ-SiW 10 O 36 {Al(OH 2 )} 2 (μ-OH) 2 ].4H 2 O, [32] WO 3 /SiO 2 /Al 2 O 3 (W25 IMP), [33] HS-AlF 3 , [34] NbÀ AlF 3 À OH, [35] Eco-Mn 1 , [36] zeolite (H-BEA), [37] zeolite (ZSM-5) [38] was developed to improve selectivity for formation of (À )-isopulegol in the cyclisation of (+)-citronellal. The Table 1 summarised the results.…”

Corymbia citriodora: A Valuable Resource from Australian Flora for the Production of Fragrances, Repellents, and Bioactive Compounds

“…Similarly, Dongil and coworkers have investigated carbon nanotubes treated with nitric acid in toluene as sustainable catalysts resulting in 100 % conversion and 97-98 % selectivity to 2 [84], although they began the process with racemic 1 and did not control for stereoselectivity in the final product. Further examples of unique approaches to the cyclization of 1 to 2 include the use of Lewis acids [85], ZnBr 2 [50,83], metal fluorides [86], hydrous zirconia [87], zeolites [88], mesoporous materials [89], SiO 2 [90], and supramolecular assemblies [91]. The use of a single multifunctional catalyst capable of achieving cyclization of starting material and hydrogenation as part of a one-or two-step process to 7 may simplify the overall menthol synthesis process.…”