Intramolecular ortho Photocycloaddition of 4-Substituted 7-(4′-Alkenyloxy)-1-indanones and Ensuing Reaction Cascades

TL;DR

This paper explores how UV light triggers complex chemical reactions in specific indanone compounds, leading to the formation of new molecules through multiple steps.

Contribution

The study introduces new reaction cascades initiated by intramolecular photocycloaddition in substituted 1-indanones under UV irradiation.

Findings

4-Chloro compounds form pentacyclic products via a three-photon cascade at 366 nm UV light.

Oxygenated substrates undergo a two-photon cascade involving ortho photocycloaddition and ring opening.

A di-π-methane rearrangement occurs in toluene under 350 nm irradiation with moderate yields.

Abstract

4-Substituted 7-(4′-alkenyloxy)-1-indanones were
prepared
from the respective substituted aryl propanoic acids and subjected
to UV-A irradiation (λ = 350 or 366 nm). While the 4-chloro
compound was directly converted at λ = 366 nm into a pentacyclic
product (47% yield) by a three-photon cascade process, the oxygenated
substrates reacted in trifluoroethanol at λ = 350 nm by a two-photon
cascade, involving an ortho photocycloaddition, a
thermal disrotatory ring opening, and a [4π] photocyclization
(six examples, 67–82% yield). An ensuing photochemical di-π-methane
rearrangement of the latter products was achieved by irradiation at
λ = 350 nm in toluene (five examples, 36–70% yield).
The diastereoselectivity of the reaction was probed employing a chiral
1-indanone with a stereogenic center at carbon atom C3. 1-Indanones
with a 4-hexenyloxy side chain [(E)- or (Z)-configured] at carbon atom C7 served to interrogate the
stereospecifity of the reaction.

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