References
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- Benkeser , R. A. and Belmonte , F. G. J. Org. Chem. , In Press
- Dauben , W. G. , Martin , E. C. and Fonken , G. J. 1958 . J. Org. Chem. , 23 : 1205
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- Criegee , R. and Schnorrenberg , W. 1949 . Justus Liebigs Ann. Chem. , 563 : 93
- Benkeser , R. A. , Robinson , R. E. , Sauve , D. M. and Thomas , O. H. 1954 . J. Am. Chem. Soc. , 76 : 631
- Benkeser , R. A. , Robinson , R. E. , Sauve , D. M. and Thomas , O. H. 1955 . J. Am. Chem. Soc. , 77 : 3230
- Christol , H. , Jacquier , R. and Mousseron , M. 1957 . Bull. Soc. Chim. Fr. , : 1027
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- Benkeser , R. A. and Kaiser , E. M. 1964 . J. Org. Chem. , 29 : 955
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- References 2b, 3,4b,5 and 6 contain the better preparations of these compounds
- Brown , H. C. 1962 . “Hydroboration” , 191 New York, N. Y. : W. A. Benjamin .
- The calcium alkylamide(s) formed during reduction catalyze reaction between calcium and the mixed-amines, thus forming more calcium-alkylamide at an increased rate. This competing side reaction for calcium necessitates the need for an excess of the metal (R. A. Benkeser and A. Rappa, unpublished results)
- Brown , H. C. and Geoghegan , P. Jr. 1967 . J. Am. Chem. Soc. , 89 : 1522 It is believed that the less sterically hindered isomer under goes selective oxymercuration-demercuration preferentially. For pertinent references see:J. Chatt, Chem. Rev., 48, 7 (1951)
- The alcohol formed is held up on the column longer
- This was true for reduction of tetralin and p-xylene. However, it appears that reductions in ethylenediami ne alone are less selective and tend to yield complex mixtures. This point is currently under investigation.
- When reductions are carried out in ethylenediami ne alone, unreacted calcium usually remains which has a dark coating on its surface. A larger excess of calcium than is used in the mixed-amine solvent system seemingly compensates for this.
- The remainder consisted of other reduction products.
- See ref. 2c for a possible explanation of why the diene forms instead of the monoene product.
- This compound should be stored under nitrogen to prevent aromatization of the diene ring by what appears to be air oxidation.
- A smaller excess of calcium results in more unreacted durene.
- Under-reduction results when less calcium is used.
- Still , W. C. , Kahn , M. and Mitra , A. 1978 . J. Org. Chem. , 43 : 2923
- Reductions in methylamine alone result in incomplete reduction often affording considerable amounts of unreacted starting material.
- In the mixed-amine solvent system the calcium (even when in excess) is always totally consumed.
- All melting points were recorded on a Mel-Temp apparatus and are uncorrected. All gas Chromatographie analyses in which a capillary instrument was used were carried out on a Varian Model 3700 instrument. Standard Chromatographic analyses were performed on a Varian Aerograph 1400 instrument. The 1 H NMRspectra were recorded on a Perkin Elmer R-32 spectrometer operating at 90 MHz in 5 mm tubes. The 13C NMR spectra were obtained on a Varian XL-200 spectrometer operating at 50.3 MHz in 10 mm tubes. All chemical shifts are reported in ppm relative to TMS. The 13C NMR spectra (50.3 MHz) were recorded with spectral widths of 10,000 Hz and 16,000 data points zero filled to 32K. The calcium shot (99.5% pure) used in all of this work was purchased from Alfa Products.
- A dry ice-acetone condenser works equally well.
- Induction periods of from several minutes to several hours have been observed for this reduction. Once the reaction starts, various color changes occur until a gray color forms. Once gray (due to a gray solid),26 this color persisted throughout the remainder of the reaction.
- If necessary, the reaction is kept from becoming too vigorous by placing dry ice around the flask. Excessive cooling will cause the reaction to stop, however, it will resume after cooling is discontinued.
- A gray solid forms over the course of the reaction and is believed to be a calcium-alkylamide. This solid is pyrophoric when dry.