Oxidative Rearrangements of Tricyclic Vinylcyclobutane Derivatives

Abstract

Three tricyclic vinylcyclobutanes (3‐methylenetricyclo[5.3.0.02,6]decanes 1–3) have been subjected to ionization by photoinduced electron transfer in solution and by X‐irradiation in Ar matrices. All three compounds undergo oxidative cycloreversion; the cleavage of the four‐membered ring, however, occurs in a different direction depending on the presence of a methyl group in position 6 of the tricyclic framework. In those derivatives, cycloreversion is found to lead to 1‐methyl‐8‐methylene‐1,6‐cyclodecadiene radical cations (5.+ from 1, 8.+ from 2) which upon back electron transfer yield two different hydrocarbons (6 from 5.+, 9 from 8.+), depending on the configuration around the endocyclic double bonds of the respective cyclodecadiene derivative. In the absence of a methyl group on C6, the cycloreversion leads to a radical cation complex between 1‐methylenecyclopent‐2‐ene and cyclopentene (12.+) which appears to revert to 3 on back electron transfer. The intermediate radical cations 5.+, 8.+, and 12.+ have been identified and characterized by UV/Vis and IR spectra in Ar matrices. The mechanism of their formation is elucidated by quantum chemical calculations.

Reaction mechanisms : Part (i) Radical and radical ion reactions

“…One electron oxidation of strained hydrocarbons (e.g., Dewar benzene, vinylcyclopropanes, etc.) can lead to a host of interesting radical ion rearrangements, as illustrated by the one electron oxidation of 3 (Scheme 30), reported by Mattay, Bally et al 105 The interested reader is directed towards the pertinent references for additional details. [105][106][107][108] The one electron reduction of ketones (either chemically or via photo-induced electron transfer, PIET) results in many of the radical-type reactions discussed in this review including additions, cyclizations, fragmentation, group transfer, etc.…”

Photochemistry of Reactive Intermediates

“…In this way we have studied several photoinduced ring-opening reactions of radical cations containing three- [17][18][19][20][21] or four-membered rings [22][23][24][25], phototautomerizations of ionized ketones and enols [26][27][28], and rotamer inter-conversions in polyene radical cations [29][30][31]. I will use two examples to illustrate the photochemistry of radical cations:…”