The intramolecular photocycloaddition of aryl aldehydes containing allene side chains is a versatile reaction as it provides a rapid and efficient access to original complex structures such as 1,3,4-tetrahydro-1,4-epoxy-5-alkylidene-2-benzoxepines 2 and substituted 2-oxa-tricyclo[5.2.2.0] 1,5 undeca-4,8,10-triene-9-carbaldehydes 3. Novel polycyclic structures are characterized, and optimized strategies for the synthesis of the substrates 1 are described.Creating complexity by the formation of new cores, stereocenters, and strained rings in one step from simple precursors is one of the many challenges of organic chemistry. Photochemistry is particularly attractive from this perspective because it may provide access to polycyclic structures without the need of aggressive reagents such as oxidants, reductants, acids, and bases. Tandem photocycloaddition/ fragmentation reactions and their applications in synthesis have been widely reviewed, but there is still a considerable potential for discovery. 1 In the past few years, we have been interested in the formation of unusual ring systems. The 1,4-cycloaddition of alkenes with arenes (para cycloaddition) has been well documented, but the similar process with allenes is much less understood. Our interest has focused on the photochemical reactivity of aryl aldehydes containing an allene side chain. In particular, when the substrate contains an aldehyde, the competition with a Paternò-Büchi-type reaction has to be considered. We report here the photochemical reactivity of ortho-allenyl benzaldehydes.For this purpose, we prepared the o-allenyl-benzaldehyde 6a-f substrates (Scheme 1) following a strategy described

In the present work, we report on a new intramolecular para-cycloaddition of arenes with allenes

Bridged compounds Q 0060Photochemistry of Allenyl Salicylaldehydes. -The reaction affords oxygen-containing tricycles and epoxy-bridged benzoxepines. -(BIRBAUM, F.; NEELS, A.; BOCHET*, C. G.; Org. Lett. 10 (2008) 15, 3175-3178; Dep. Chem., Univ. Fribourg, CH-1700 Fribourg, Switz.; Eng.) -Klein 47-072

A novel intramolecular para cycloaddition of arenes with allenes yielding bicyclooctadiene‐type products and benzoxepine acetals is presented.