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The synthesis and reactions of simple derivatives of 2(3H)- and 3(2H)furanones
have attracted considerable attention in recent years, primarily in
connection with development of routes to antitumor agents that contain this
ring as central structural unit. They also serve as useful synthetic building
blocks for lactones and furans and are the precursors of a wide variety of
biologically important heterocyclic systems. Although a number of syntheses
of furanones were known they were in many cases limited to specific
substitution pattems. The development of altemative strategies for the
preparation of these heterocycles is therefore of considerable importance or
continues to be a challenge.We propose to develop new and general approaches to the synthesis of
furanone ring systems from simple and readily available starting materials
since we were interested in examining their rich photochemistry. The
photochemical reactivity of Beta,gama-unsaturated lactams and lactones is a subject of current interest. Some of the prominent photoreaction pathways of
unsaturated lactones include decarbonylation, solvent addition to double
bonds, decarboxylation, migration of aryl substituents and dimerisation. lt
was reported earlier that the critical requirement for clean photochemical
cleavage of the acyl-oxygen bond is the presence ofa double bond adjacent to
the ether oxygen and 2(3H)-furanones possessing this structural requirement
undergo facile decarbonylation. But related phenanthrofuranones are isolated
as photostable end products upon irradiation. Hence we propose to synthesis a
few phenanthro-2(3H)-furanones to study the effect of a radical stabilising
group at 3-position of furanone ring on photolysis. To explore the tripletmediated
transformations of 2(3H)-furanones in polar and nonpolar solvents a
few 3,3-bis(4-chlorophenyl)-5-aryl-3H-furan-2-ones and 3,3-di(p-tolyl)-5-aryl-
3H-furan-2-ones were synthesised from the corresponding
dibenzoylstyrene precursors by neat thermolysis. Our aim was to study the
nature of intermediates involved in these transformations.We also explored the possibility of developing a new and general
approach to the synthesis of 3(2H)-furanones from simple and readily
available starting materials since such general procedures are not available.
The protocol developed by us employs readily available phenanthrenequinone
and various 4-substituted acetophenones as starting materials and provides
easy access to the required 3(2H)-furanone targets. These furanone
derivatives have immense potential for further investigations .We also aimed the synthesis of a few dibenzoylalkene-type systems
such as acenaphthenone-2—ylidene ketones and phenanthrenone-9-ylidene
ketones. These systems were expected to undergo thermal rearrangement to
give furanones and spirofuranones. Also these systems can be categorised as
quinonemethides which are valuable synthetic intermediates. |
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