(Chief Bee)
06-12-02 01:13
No 319960
      Dimethyldioxirane epoxidation of anethole/asarone
(Rated as: good read)

Synthesis of trans-anethole oxide and trans-asarone oxide
Carcinogenesis 20(7), 1303-1307 (1999)


Dimethyldioxirane solution in acetone was made freshly by an improved conventional method [1]. After the solution was dried with molecular sieves (4 Å, activated powder), it was titrated iodometically with KI and starch. The titrated dimethyldioxirane solution (~0.08 M solution in acetone, 1.2 equiv.) was added to trans-anethole or trans-asarone in dry acetone (1 ml for 1 mmol) at 0°C and the reaction mixture was stirred for 30 min at room temperature. The reaction solution was evaporated under reduced pressure to afford the epoxides. trans-anethole oxide was a colorless oil. The yellow oil of trans-asarone oxide after vacuum application was dissolved in dry hexane and recrystallized at –20°C for a few days to produce a white solid product (mp. 37–40°C). The yields of these oxides were >95%. The oxides were kept at –80°C in dry nitrogen. In this condition trans-anethole oxide was stable for 1 year and trans-asarone oxide was stable for 1 month.

Purity of trans-anethole oxide and trans-asarone oxide

trans-anethole oxide and trans-asarone oxide were found to have very pure NMR spectra with little or no impurity peaks. The yields of oxides from this method were >95%, which are much better than those of Mohan and Whalen [2] and Greca et al. [3] whose methods used m-chloroperoxybenzoic acid to oxidize anethole or asarone and gave yields of 38 and 52%, respectively.

Stability of trans-anethole oxide and trans-asarone oxide

Both of the oxides were stable in acetone or DMSO for 1 h at 0 or 37°C. In aqueous environments, however, the amount of these epoxides declined, presumably because of their hydration to diols. The half-life of trans-anethole oxide was 7.6 min in 0.1 M potassium phosphate buffer (pH 7.4) at 37°C. The presence of 154 mM KCl lowered the half-life to 4.2 min. Trans-asarone oxide showed shorter half-lives; 4.0 min without or 2.4 min with 154 mM KCl.

[1] Ber., 124, 2377
[2] JOC 10, 2663-2669
[3] Phytochemistry 28, 2319-2321
(Chief Bee)
09-27-04 20:02
No 533411
      Org. React. 61: Dioxirane Epoxidation of Alkenes
(Rated as: excellent)

If anyone has access to the full version of Organic Reactions online, feel free to post the missing tables not available in the DjVu file below.

Dioxirane Epoxidation of Alkenes
Waldemar Adam, Chantu R. Saha-Möller, Cong-Gui Zhao, John Wiley & Sons, Inc. (2002)
Org. React. 61, Chapter 2, pp. 219-264 + 508-516 (../rhodium/djvu /or61.dioxirane.epoxidation.adam.djvu) (sans tables, provided by lugh)

1. Introduction
2. Mechanism
3. Scope and Limitations
4. Comparison with Other Methods
5. Experimental Conditions
6. Experimental Procedures
7. Tabular Survey
8. Acknowledgments

Keywords: dioxirane; epoxidation; alkenes; unfunctionalized alkenes; electron-rich; electron poor; electron donor; electron acceptor; chemoselectivity; regioselectivity; diastereoselectivity; entioselectivity; scope; limitations; oxidation; solvents; temperature; neutral conditions; basic conditions; homogeneous media; comparison of methods; experimental conditions; experimental procedures; tabular survey

An ideal oxidant should be highly reactive, selective, and environmentally benign. It should transform a broad range of substrates with diverse functional groups, preferably under catalytic conditions, and be readily generated from commercially available and economical starting materials. Of course, such an ideal oxidant has not yet been invented; however, the dioxiranes, which have risen to prominence during the past few decades, appear to fulfill these requirements in many respects. These three membered ring cyclic peroxides are very efficient in oxygen transfer, yet very mild toward the substrate and product. They exhibit chemo-, regio-, diastereo-, and enantioselectivities, act catalytically, and can be readily prepared from a suitable ketone (for example, acetone) and potassium monoperoxysulfate (2KHSO5·K2SO4·KHSO4, Caroate®, Oxone®, or Curox®), which are low-cost commercial bulk chemicals. Throughout the text KHSO5 is used to specify this oxygen source, rather than refer to one of the commercial trade names.

The Hive - Clandestine Chemists Without Borders