Photoirradiation of 3-alkoxy-6-chloro-2-(2'-furyl) -4-0x0-4H-1 -benzopyrans 3 led to the formation of methyl 8-chloro-1 O-oxo-2-phenyl-2,3,4,1 O-tetrahydropyrano[3,2-b] [l 3 benzopyran-3-ylacetate 4.The reaction proceeds through the formation of 8-chlor0-4-phenyl-3a,4,6,11 b-tetrahydrofuro-[2'.3':4,5]pyrano[3.2-b] benzopyran-6-one 5a, which subsequently undergoes a ring contraction-ring expansion mechanism to give the cyclopropanecarbaldehyde 8 followed by its rearrangement to ketene 10 via the carbene 9 to furnish ester 4. The various intermediates have been isolated and identified, and their stereochemistry was established from their 'H NMR spectra.Conjugated enones with suitable substituents at the a-position, when subjected to photolysis, are known to undergo y-H abstractions.' The products obtained depend invariably upon the nature of the substituents present in the substrates: viz. 2alkyl-3-arylcyclohex-2-enones and 3-alkoxy-2-phenyl-4-oxo-4H-1 -benzopyrans afforded photocyclised angular products whereas 3-benzyloxy-2-styrylchromones,4 upon exposure to W light, yielded tricyclic linear products. In contrast 3methoxy-2-methylchromone has been found to lead to the formation of a novel dimeric oxetanol.' It thus became of interest to investigate the photochemistry of 3-alkoxychromones bearing a fury1 group instead of a Me, Ph or CH=CHPh at C(2), since furans themselves are known to undergo phototransformations.6 Such a system allows another dimension, here, to be studied as it becomes a bichromophoric system, an enone coupled to a furan. Results and DiscussionThe target molecules, i.e., 2-(2'-furyl)-3a ' and 2-(5'-methyl-2'furyl)-3-benzyloxy-4-oxo-4H-1 -benzopyran 3b were synthesised as follows (Scheme 1).Photoirradiation of 3a in methanol produced ester 4, whose structure became evident from its 'H NMR and mass spectra. The 'H NMR spectrum (100 MHz) of compound 4 showed a

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Photocyclisation of 3-alkoxy-2-arylthiochromones leads to angular tetracyclic compounds through H-abstraction that requires activation by a phenyl group.