A new cyclization reaction by tris(triphenylphosphine)rhodium chloride.

Vapor‐Phase Reaction of Citronellal over Mesoporous Molecular Sieves MCM‐41 and Zeolites

“…15 With a superacid such as FSO 3 H/SO 2 , IPG and neoisopulegol were produced via cyclization that followed the same reaction path as the normal acids. 8 For this reaction over Al2O3, SiO 2 -Al 2 O 3 , TiO 2 -ZrO 2 , FeSO 4 , NiSO 4 , Ti(SO 4 ) 2 and Zr(SO4)2, the CTN conversion and IPG selectivity were 65-91% and > 91%, respectively. On the contrary, CaO exhibited little activity that was attributed to its low Lewis acidity.…”

“…The conversion of citronellal (CTN) to isopulegol (IPG) over acid catalysts has drawn much attention in both academic and industrial research because IPG is an important intermediate for the synthesis of menthol, a raw material for the manufacture of pharmaceuticals, cosmetics, flavors, and toothpastes. 1 This reaction was traditionally performed in the liquid phase using various homogeneous or heterogeneous catalysts such as aqueous sulfuric acid, 2 acetic anhydride, 3 tris(triphenylphosphine) rhodium chloride, 4 molybdenum and tungsten carbonyl complexes, 5 scandium trifluoromethanesulfonate, 6 heterogeneous Lewis acid, 7 superacids, 8 single or mixed metallic oxides, [9][10][11] metal salts, 7,9 micellar catalysts, 12 zeolites, 13 sulfated zirconia-carbon molecular sieve composite catalysts 14 as well as hydrous zirconia and clays. 15 With a superacid such as FSO 3 H/SO 2 , IPG and neoisopulegol were produced via cyclization that followed the same reaction path as the normal acids.…”

2.03 Prins Reactions and Carbonyl, Imine, and Thiocarbonyl Ene Reactions

“…However, Sakai found that use of Wilkinson's catalyst (Rh(PPh 3 ) 3 Cl) gives a 25:75 mixture of isopulegol (162a) and neoisopulegol (162b). 128 Other bulky Lewis acids such as NbCl 5 give mixtures rich in 162b and Bn(Et) 3 N þ [Mo(CO) 4 ClBr 2 ] À gives a 25:75 mixture favoring 162b. 129 Kočovský suggested that with small Lewis acids cyclization occurs preferentially through chair transition state 164 to give 162a, whereas with large Lewis acids this transition state is disfavored by steric interactions between the Lewis acid and alkene substituents so cyclization occurs through boat transition state 165 to give 162b.…”

The Prins and Carbonyl Ene Reactions

“…69 Zinc bromide was shown to be an optimal Lewis acid catalyst giving a 66:4:0:0 mixture of adducts'?o Use of Wilkinson's catalyst gives a 14:41 :0:0 mixture of products, although the reasons for this stereocontrol are not understood. 71 Oxidation of citronellol with PCC gives (85), which undergoes an acid or Lewis acid catalyzed cyclization to (86)- (89). Further oxidation by PCC and conjugation of the double bond gives pulegone.…”