The reaction of 2,2-dialkoxycyclopropane-1-carboxylates 1a–d and monoalkoxycyclopropane 1e with NOCl gives isoxazoline- and/or isoxazole-3-carboxylates by regioselective ring-opening at C1–C2 bond. A mechanistic interpretation suggests the intermediacy of well-stabilised dipolar species.
GrazianoM.L., and PiccialliV., Tetrahedron Lett., 1999, 40, 8469.
9.
PiccialliV., and GrazianoM. L., Tetrahedron Lett., 2001, 42, 93.
10.
(a) KimE.K., and KochiJ. K., J. Am. Chem. Soc., 1991, 113, 4962.
11.
ShabarovY.S., SaginovaL. G., and GazzaevaR. A., Khim. Geterotsikl. Soedin., 1983, 6, 738; Chem. Abstr. 1983, 99, 139831.
12.
LoeppkyR.N., and ElomariS., J. Org. Chem., 2000, 65, 96.
13.
LinS.-T., KuoS.-H., and YangF.-M., J. Org. Chem., 1997, 62, 5229.
14.
MizunoK., IchinoseN., TamaiT., and OtsujiY., J. Org. Chem., 1992, 57, 4669.
15.
Strictly anhydrous conditions were necessary especially for cyclopropanes 1a–d. They react easily with protic agents as H2O,11a alcohols,11b hydrogen halides,1,5 (with 1a>1b>1c>1d) leading to open-adducts which decompose to ethyl methyl butanedioates. So, the latter may be present occasionally in the reaction mixtures. (a) M.L. Graziano and R. Scarpati, J. Chem. Soc., Perkin Trans. 1, 1985, 289; (b) GrazianoM.L., and IesceM. R., Synthesis, 1985, 762.
AuricchioS., RiccaA., and de PavaO. V., J. Org. Chem., 1983, 48, 602.
18.
The low reactivity of C3 disubstituted cyclopropanes 1 was already observed (see ref. 5a and references therein).
19.
ScarpatiR., and SperoniG., Gazz. Chim. Ital., 1959, 89, 1511.
20.
SN2-type displacement by the halide has been suggested in the reactions of 1 and 6 with sulfenyl5a and selenenyl1 chlorides and the related alkyl chlorides, so formed, have been spectroscopically evidenced. Although a similar pathway could be invoked in the formation of 4d directly from 8d, it appears less probable than the acid-catalysed hydrolysis of isoxazoline 3d since no oximes as 4 were found even for entries a–c. Evidently in these cases cyclization surpasses completely the SN2 displacement.
21.
Mass balance for the reaction indicated a loss of material, and this trend which was also observed in previous cases,5b may be due to the volatility of the products.
22.
Cyclopropanes as 1 can be efficiently prepared by reaction of alkyl diazoacetate with ketene acetals or vinyl ethers under copper catalysis (See ref. 2).
23.
(a) SutharchanadeviM., and MuruganR.: in Comprehensive Heterocyclic Chemistry II (ShinkaiI. (ed.)), Elsevier Science, Oxford, 1996, Vol. 3, pp. 221–260.
24.
LangS.A., and LinY.-I: in Comprehensive Heterocyclic Chemistry, (KatritzkyA.R., and ReesC. W. (eds)), Pergamon Press, Oxford, 1984, Vol. 6, pp. 1–130.
