Oxa-di-π-methane Photochemical Rearrangement of Quinuclidinones. Synthesis of Pyrrolizidinones

Abstract

[reaction: see text] The oxa-di-pi-methane (ODPM) photochemical rearrangement, a triplet-sensitized sigmatropic 1,2-acyl shift of beta,gamma-enones, was successful utilizing methyl and heptyl 1-aza-3-carboalkoxybicyclo[2.2.2]oct-2-en-5-ones (quinuclidinones) as the photoprecursors. The cyclopropane of the heptyl ester tricyclic photoproduct could be opened with lithium dimethylcuprate or via hydrogenolysis to produce the corresponding pyrrolizidinone skeletons.

5.06 Di-π-methane, Oxa-di-π-methane, and Aza-di-π-methane Photoisomerization

“…78 A straightforward access to this skeleton involving ODPM photoisomerization of nitrogen containing bicyclic systems was proposed (Scheme 26). 79 The 1-aza-3-carboalkoxybicyclo[2.2.2]oct-2-en-5-one (quinuclidinone) 120 serving as the photoprecursor was synthesized according to previously described procedures. The photochemical irradiation (using a 450 W medium-pressure lamp) of a solution of compound 120 in acetophenone or 5/95-acetophenone/acetone afforded the ODPM product 121 in 70% yield.…”

Cycloaddition of Spiroepoxycyclohexa-2,4-dienones, Radical Cyclization and 1,3-Acyl Shift in Excited State: Aromatics to Sterpuren-4-one

“…After having developed synthesis of the key tricyclic compounds 3a , b endowed with a β,γ-enone chromophore, their photochemical reaction was examined. Photoreactions of β,γ-enones have generated interest for a long time that has further enhanced due to their synthetic potential. − Rigid β,γ-enones generally undergo a 1,2-acyl shift or oxa-di-π-methane rearrangement upon sensitized irradiation (triplet excited state) whereas direct irradiation (singlet excited state) results in a 1,3-acyl shift. While, a large number of examples of 1,2-acyl shift or oxa-di-π-methane reactions have been reported, studies on 1,3-acyl shift are limited.…”

13 Organic photochemistry

“…52 The oxa-dip-methane rearrangement of quinuclidinones 68 gave tricyclic compounds 69 (Scheme 33). 53 Subsequent reaction of the cyclopropyl ring of 69 led to the pyrrolizidinone skeleton 70. Irradiation of bicyclo[2.2.2]octenone 71 at 300 nm, leads to low yields of the oxa-di-p-methane product 72, as well as the 1,3-acyl shift product 73, while lower wavelength irradiation improves the yield of 72 (Scheme 34).…”