Photochemical transformations of small ring carbonyl compounds. XXXIX. Photochemical synthesis and chemical reactivity of the tricyclo[3.2.0.02.6]heptan-7-ol system

Abstract

The photolysis in benzene of exo-5-benzoylbicyclo[2.1 .ljhexane (4) has been found to afford A2-cyclopentenylacetophenone (5) and 7-phenyltricyclo[3.2.0.02|6]heptan-7-ol (6). The formation of these products is considered to proceed through a diradical intermediate formed by transannular hydrogen abstraction by the excited n-ir* triplet state. The tricyclic alcohol was found to rearrange thermally to 4 and 5. The rearrangement to 4 was shown to proceed via cleavage of the bridgehead carbon-carbon bond followed by 1,5-H transfer. In basic media the tricyclic alcohol isomerized to ex:o-5-benzoylbicyclo[2.1.1 ]hexane with overall retention of configuration. The tricyclic alcohol was also found to be extremely unstable to acidic conditions and rearranged to 2-phenyl-anff-7-norbornenol. The rearrangement was rationalized as proceeding via a tricyclo[3.2.0.02'7]heptyl cation.

Acid homoketonization with inversion of configuaration. Dramatic effect of water in control of stereochemistry

“…This seemingly novel isomerization may proceed via the intermediate 16. Gas chromatography revealed crude synthetic -sinensal (1) to contain 10% of the bicyclic aldehydes 11 resulting from intramolecular Diels-Alder reaction of 9 and approximately 5% of what may be the A6-cis isomer formed in the Cope rearrangement. 15 Infrared, mass, ultraviolet, and proton spectra of distilled material, bp 82°( 0.1 mm), were identical with those of natural -sinensal (1) and a mixture of the synthetic 2,4-dinitrophenylhydrazone mp 98-100°and the "natural" derivative mp 100-102°melted at 98-101°.…”

Orbital‐Overlap Control of the Reactivity of a Bicyclic 1‐Hydroxy‐1,4‐Biradical

“…We are not the first to study biradicals of types 1 and 2 . The solution‐phase behavior of biradical 2 (Ar=Ph) was reported in 1972 by Padwa and Eisenberg and shown to consist of 66 % cleavage and 30 % cyclization 9. Similarly, Alexander and Uliana showed in 1976 that, in solution, biradical 1 (Ar=Ph) bearing a phenyl substituent at the C2 position undergoes 100 % cyclization 10.…”

Solid‐State Asymmetric Photochemical Studies Using the Ionic Chiral Auxiliary Approach

“…Based on the work of Padwa and Eisenberg in 1972, [46] Yang, Xia, Scheffer, Botoshansky, and Kaftory synthesized bicyclo [1.1.1] and [2.1.1] derivatives and equipped them with a carboxylic acid substituent in the para position of the aryl ketone group for asymmetric study (Scheme 12). [47] Treatment of carboxylic acid 30 a with a variety of optically pure amines gave salts of the general structure 30 b. Irradiation of crystals of the salts followed by diazomethane workup yielded the cleavage product 31 c, which was analyzed by HPLC for enantiomeric excess; the results are summarized in Table 4.…”