1.
All glassware was flame-dried under vacuum and allowed to cool under an atmosphere of nitrogen.
2.
Rhodium (II) acetate dimer was purchased from Strem Chemicals. It was stored and weighed in a glove box and was used without further purification.
3.
Triphenylacetic acid (99%) and chlorobenzene (99%) were purchased from Aldrich Chemical Company, Inc. and used as received.
4.
Slow distillation of the solvent (bp 132 °C) removes the acetic acid (bp 117 °C) formed from the ligand exchange. If the distillation rate is higher than 10 mL/hour, chlorobenzene is added in order to keep the total volume of the reaction mixture over 40 mL.
5.
The solid is insoluble in methanol and the color changes from green to purple-blue.
6.
A half-scale run provided 1.75 g (89%) of the rhodium II tetrakis(triphenylacetate) dimer.
7.
Analytical data for Rhodium II tetrakis(triphenylacetate) dimer (2): Rf = 0.19 (10% ethyl acetate/hexane); 1H NMR pdf (300 MHz, CDCl3) δ: 3.51 (residual MeOH), 6.63 (d, J = 7.5 Hz, 24 H), 6.86 (t, J = 8.1 Hz, 24 H), 7.07 (t, J = 7.5 Hz, 12 H); 13C NMR pdf (75 MHz, CDCl3) δ: 69.2 (residual MeOH), 126.8, 127.4, 130.7, 143.4, 192.9; IR (film) 3055, 1590, 1580, 1365 cm-1; Analysis calc. for C80H60O8Rh2: C 70.90, H 4.46; found: C 67.96, H 4.73 %. The low value obtained for the carbon analysis is due to residual coordinated methanol from the recrystallization. Up to 2 equiv of MeOH per molecule of dimer (determined by 1H NMR, δ = 3.51 and 13C NMR, δ = 69.2) can be present and do not affect the reactivity of the catalyst.
8.
1,1'-Carbonyldiimidazole, reagent grade, was purchased from Aldrich Chemical Company, Inc. It was stored and weighed in a glove box to avoid hydrolysis and was used without further purification.
9.
Short exposure to 1,1'-carbonyldiimidazole could cause serious temporary or residual injury. This reagent should be handled with careful attention to avoid contact with skin.
10.
Acetonitrile was distilled over calcium hydride. If wet acetonitrile is used, hydrolysis of a reaction intermediate reduces the yield.
11.
Cyclohexanemethanol (3), 99+%, was purchased from Aldrich Chemical Company, Inc. and was used as received.
12.
Hydroxylamine hydrochloride (99%) and imidazole (99%) were purchased from Alfa Aesar and used as received.
13.
An excess of hydroxylamine and imidazole is used in order to accelerate the reaction and minimize the hydrolysis of the intermediate.
14.
The 1H NMR pdf methylene resonances of the N-hydroxycarbamate (doublet at 3.96 ppm) and the starting alcohol (doublet at 3.44 ppm) are used to determine the product ratio.
15.
Flash chromatography is performed on a 3 × 10 cm silica gel column (33 g of dry silica). The product is charged on the column and the system is eluted with 50 mL of 20% ethyl acetate-dichloromethane. At that point, fraction collection (8-mL fractions) is begun and elution is continued with 450 mL of a 20% ethyl acetate-dichloromethane mixture. Collected fractions were analyzed by TLC, eluting with 30% ethyl acetate-dichloromethane (Rf = 0.52 for 4 and 0.63 for 3). Visualization was accomplished by spraying with a potassium permanganate solution followed by heating. All the fractions (10-30) containing the desired product were combined and concentrated at 45 °C by rotary evaporation (40-50 mmHg) and then at 0.5 mmHg.
16.
Analytical data for cyclohexylmethyl N-hydroxycarbamate (4): mp 33-34 °C; 1H NMR pdf (300 MHz, CDCl3) δ: 0.85-1.04 (m, 2 H), 1.06-1.37 (m, 3 H), 1.40-1.90 (m, 6 H), 3.99 (dd, J = 6.3, 5.1 Hz, 2 H), 7.03 (br s, 1 H), 7.28 (br s, 1 H); 13C NMR pdf (75 MHz, CDCl3) δ: 25.7, 26.4, 29.6, 37.4, 71.5, 159.9; IR (film) 3291, 2922, 2851, 1712, 1449, 1267, 1121 cm-1; HRMS (TOF+) calc. for C8H15NO3Na [M+Na]+: 196.0950; found: 196.0940; Analysis calc. for C8H15NO3: C 55.47, H 8.73, N 8.09; found: C 55.49, H 8.81, N 7.93 %.
17.
Anhydrous diethyl ether was obtained by filtration through a drying column on a Sol-Tec solvent purification system.
18.
p-Toluenesulfonyl chloride, 99+%, was purchased from Aldrich Chemical Company, Inc. and was used as received.
19.
Triethylamine was purchased from Fisher Scientific and was freshly distilled from CaH2 (88-90 °C) under argon atmosphere prior to use.
20.
UltraPure silica gel (32-63 μm) was purchased from EcoChrom.
21.
Omnisolv grade hexane was purchased from EMD and was used as received.
22.
A second run on approximately half-scale provided a 79% yield.
23.
The physical properties of 5 are as follows: Rf 0.68 (5% ethyl acetate/dichloromethane); mp 88-90 °C; 1H NMR pdf (500 MHz, CDCl3) δ: 0.82-0.85 (m, 2 H), 1.0-1.3 (m, 3 H), 1.46-1.57 (m, 3 H), 1.63-1.67 (m, 3 H), 2.46 (s, 3 H), 3.83 (d, J = 6.3 Hz, 2 H), 7.35 (d, J = 8.1 Hz, 2 H), 7.87 (d, J = 8.1 Hz, 2 H); 13C NMR pdf (125 MHz, CDCl3) δ: 21.9, 25.7, 26.3, 29.3, 37.1, 72.2, 129.7, 129.9, 130.5, 146.2, 155.9; IR (film) 3230, 2927, 2853, 1740, 1597, 1380, 1191, 1179 cm-1; HRMS (TOF+) calc. for C15H21NO5SNa [M+Na]+: 350.1038; found: 350.1006; Analysis calc. for C15H21NO5S: C 55.03, H 6.47, N 4.28, S 9.79; found: C 54.85, H 6.30, N 4.11, S 10.07 %.
24.
Dichloromethane was purchased from Fisher Scientific and was used as received.
25.
Granular potassium carbonate was purchased from J.T. Baker and was used as received.
26.
The total volume added is approximately 60 mL.
27.
Analytical data for 3-oxa-1-azaspiro[4.5]decan-2-one (6): Rf 0.53 (30% ethyl acetate/dichloromethane); mp 81-82 °C; 1H NMR pdf (300 MHz, CDCl3) δ: 1.20-1.72 (m, 10 H), 4.08 (s, 2H), 6.82 (br s, 1H); 13C NMR pdf (75 MHz, CDCl3) δ: 22.7, 24.9, 37.2, 57.9, 75.8, 159.7; IR (film) 3230, 2932, 2858, 1745, 1397, 1251, 1031 cm-1; HRMS (TOF+) calc. for C8H13NO2Na [M+Na]+: 178.0844; found: 178.0843; Analysis calc. for C8H13NO2: C 61.91, H 8.44, N 9.03; found: C 61.99, H 8.61, N 8.94 %.