References
- Department of Chemistry (D-006), University of California-San Diego, La Jolla, California 92093
- Wenkert , E. 1980 . Acc. Chem. Res. , 13 : 27
- Wenkert , E. and Buckwalter , B. L. No difficulty was encountered in a case of the ester function being one carbon closer to the reaction site in the cyclopropanation. Thus the decomposition of methyl 5-diazo-4-oxopentanoate over copper bronze in n,-butyl ether at 80°C yielded (47 %) oxycyclopropane lc, unpublished observation)
- Whereas diazomethane treatment of the crude acids afforded additional esters 2, and 3a, treatment with thionyl chloride and methanol led to 3a, and the preponderant replacement of the diketoester 2, by its dehydration product, methyl γ-(5-methylfuryl-2-)butyrate [oil: IR (CHCl3) C=0 1732 (s) cm−1; 1H NMR (CDCl3) δ 1.8–2.9 (m, 6, methylenes), 2.30 (s, 3, Me), 3.78 (s, 3, OMe), 6.05 (s, 2, aromatic Hs); m/e 182 (M+, 15 %), 151(15), 108(98), 97(40), 95 (base), 59(27), 55(32), 43(97)]
- Hydrolysis of lc3 with aqueous hydrochloric acid in THF yielded (56 %) methyl 4, 7-dioxoheptanoate
- Schenck , G. O. and Steinmetz , R. 1963 . Justus Liebigs Ann. Chem. , 668 : 19
- Novák , J. and Šorm , F. 1958 . Collect. Czech. Chem. Commun. , 23 : 1126
- At least the exo, isomers
- Wenkert , E. , Alonso , M. E. , Gottlieb , H. E. , Sanchez , E. L. , Pellicciari , R. and Cogolli , P. 1977 . J. Org. Chem. , 42 : 3945
- The sensitivity of 3a, to aqueous acid limits silica chromatography to fast operation and the use of minimal adsorbent. When in one experiment the product was left adsorbed on a dry column for l h before normal elution ca., 40% of 3a, was recovered. The remainder required elution with 50:1 CH2Cl2-MeOH, proved to be acidic and led to a 3:1 3a, 2, mixture after methylation with diazomethane. Thus the cyclopentenone ester undergoes facile retroaldol fragmentation and hydrolysis (probably assisted intramolecularly)