Page 79 - Catalysts for Fine Chemical Synthesis Vol 1 - Robert & Poignant

64 hydrolysis, oxidation and reduction

and then rapidly warmed to 0 8C by means of an ice-bath while stirring was
continued.
5. The reaction was monitored by TLC (eluent: n-hexane±diethyl ether, 8:2).
2-Isobutylidene-1-tetralone (UV active) stained light purple with p-anisalde-
hyde dip, R f 0.66 and the epoxide (UV active) dark purple, R f 0.30.
6. The reaction was quenched after 16 hours by addition of aqueous phosphate
buffer solution (pH 7, 8 mL).
It is recommended to replace the oxygen balloon for an argon balloon
after 3.5 hours; extensive exposure to O 2 can have an adverse influence on
the reaction.
7. The reaction mixture was transferred into a separating funnel and the two
layers were separated. The upper aqueous layer was extracted with dichlor-
omethane (3 30 mL). The combined organic layers were washed with
brine, dried over sodium sulfate and the solvent was evaporated under
reduced pressure.
8. The residue was purified by flash chromatography using petroleum ether±
0
0
diethyl ether (9:1) as eluent to give (2S, 3 R)-1,2,3,4-tetrahydro-3 -isopropyl-
spiro [naphthalene-2,2 -oxirane]-1-one as a yellow oil (190 mg, 0.88 mmol,
0
90 %).
The ee (>99 %) was determined by HPLC (Chiralpak 1 AD column, flow
0
1 mL/min, ethanol±n-hexane; 1:9); (2S, 3 R)-enantiomer: R t 8.84 min, (2R,
3 S)-enantiomer: R t 7.02 min.
0
1
H NMR (200 MHz, CDCl 3 ): d 8.09 (dd, J 7.7 Hz, J 1.1 Hz, 1H,
COCCH); 7.54 (td, J 7.4 Hz, J 1.6 Hz, 1H, COCCHCH); 7.34 (m, 1H,
CH 2 CCHCH); 3.15 (dd, J 8.2 Hz, J 4.4 Hz, 2H, COCCH 2 CH 2 ); 3.00 (d, J
9.3 Hz, 1H, CH 3 CHCH); 2.50 (dt, J 13.7 Hz, J 8.4 Hz, 1H, COCCH 2 ); 2.14
(dt, J 13.7 Hz, J 4.7 Hz, 1H, COCCH 2 ); 1.68 (m, 1H, CH(CH 3 ) †; 1.2 (d, J
2
6.6 Hz, 3H, CH 3 ); 2.06 (d, J 6.6 Hz, 3H, CH 3 ).
ÿ1
IR (CHCl 3 , cm ): 3009 (C±H aromatic), 2972, 2935, 2873 (C±H ali-
phatic), 1687 (C ˆ O), 1604 (C±C aromatic), 1469, 1457, 1433 (CH 2 , CH 3 ),
1316, 1304, 1203 (C±O±C), 1158, 925, 893, 878, 844, 822.
Mass: calculated for C 14 H 16 O 2 : m/z 216.11502; found [M] ‡ 216.11520.

4.3.2 CONCLUSION
Ender's method is easy to reproduce; however, it needs a freshly prepared
diethylzinc solution as its quality can dramatically influence the enantiomeric
excess. Strictly, the reaction is not a catalytic process but the methylpseudoe-
phedrine (chiral auxiliary) can be recovered almost completely with unchanged
enantiomeric purity during the flash chromatography. This method gives good
results for epoxidation of a-enones such as (E)-2-alkyliden-1-oxo-1,2,3,4-tetra-
hydronaphthalene. The enantiomeric excess obtained during the validation
correlates with the published result. Table 4.2 gives the results obtained by
the method described above, according to the relevant publication.