Pyrolytic rearrangement of two cyclobutene epoxides

Abstract

The pyrolytic rearrangement of exo-bicyclo [3.2.0] hepb6-ene oxide (1) and ero-bicyclo[4.2.0]oct-7-ene oxide (6) have been investigated. At 400°, the latter gives A2-cyclohexenylacetaldehyde (7), 1-methylcyclohexene, and 3 4-tetramethylene-2,s dihydrofuran (8). The corresponding cyclobutanones (10 and 11) were shown not to b& intermediates. The structures of the products have been assigned on the basis of comparison with authentic samples and further chemical transformations.At 420°, the former gives Az-cyclopentenylacetaldehyde (2) in 50y0 yield.

1‐Substituted 1,3‐Dihydroisothianaphthen‐2,2‐dioxides: Preparation and Use as ortho‐Quinodimethane Precursors in Intramolecular Cycloadditions. Preliminary communication

“…The minor formation of the styrene 5b3)9 (10% yield) indeed reflects the intermediacy of some (Z)-quinodimethane IV. Similar yields of 4c3) 5, ' ) and 5c3) 6, were obtained on the analogous pyrolysis4) of the homologous hexenyl-sulfone 3 c.…”

“…Having a practical route to various olefinic sulfones in hand we turned our attention to the anticipated therrnolyses I -+ I1 --f 111. a) The commercially unavailable electrophiles3) were prepared by the following standard procedures: Entry G : see [5]; entry H: tosylation (1.1 mol-equiv. of TsCVPy/25"/3 h) of the known alcohol [6]; entry I: treatment of the 2-cyclopentene-1-acetic acid (Aldrichj with an excess of (COC1)2/ CH2C1*/25°/18 h; entry J: treatment of the above acid chloride with an excess of EtOH/Py/25'/18 h. The reactions were carried out as described above for entry C unless otherwise specified; LiTMP= lithium 2,2,6,6-tetramethylpiperidide, LDA=lithium diisopropylamide, HMPT=hexamethyl-phosphoric triamide. The reaction mixtures obtained in the entries I, J, K and L were quenched with aq.…”

“…Tetracyclic systems may be readily formed when the bridge or the olefinic bond I are part of a ring as illustrated by the efficient conversions4) 3d+ 63) 5 , and + 7e3) 5 , (Scheme 5); the latter reaction again furnished the styrene 83) 6, in low yield (12%). Thermolysis of the ketone 3f in refluxing 1,2,4-triichlorobenzene gave the crystalline polyfused cyclopentanone 7f3)8) as a single stereoisomer; the corresponding isochromene VII was isolated from the reaction mixture in 41% yield.…”

Photochemical rearrangement of diene endoperoxides

“…The thermal rearrangement of epoxides to ketones has been observed as have exceptions (12), but such rearrangements are not known to occur photochemically with light of such long wavelength4 in the absence of an additional vicinal chromophore (such as a ketone carbonyl). In control experiments the bisepoxides appeared stable, which suggests that the 1,3-biradical 15 rearranges directly to the ketoepoxide at least in the photochemical process.…”

Pyrolytic rearrangement of norbornene oxide

“…The formation of cycloalkene acetaldehydes (3) from the pyrolysis of bridged cyclobutene epoxides (1) led to the consideration of a diradical intermediate 2 (1,2) (see Scheme 1). It appeared plausible that the pyrolysis of exo-2,3-epoxybicyclo [2.2.1 Iheptane (4, norbornene oxide) might give similar products via the closely related intermediate 5.…”