# 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.

## Key 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.