Site-selectivity in [2+2]-Photocycloadditions of 2H,8H-Benzo[1,2-b:3,4-b′]dipyran-2,8-dione to Alkenes†‡

Abstract

On irradiation (! 350 nm) in the presence of 2,3-dimethylbut-2-ene or 2-methylpropene the title compound 2 undergoes cycloaddition at the C(9)0C(10) double bond selectively (b15:1) to afford the 8a,9,10,10a-tetrahydro-2H,8H-cyclobuta[c]pyrano[2,3-f ][1]benzopyran-2,8-diones 3.

Recent Advances in the Synthesis of Cyclobutanes by Olefin [2 + 2] Photocycloaddition Reactions

“…602,603 The same group prepared also several coumarins with a second chromophore annulated to the arene ring of the coumarin. 604,605 The regioselectivity of the addition reactions was investigated. Benzodipyrandione 326 was found to undergo only a single [2 + 2] photocycloaddition upon direct excitation (Scheme 106).…”

Ring-closing-metathesis-based synthesis of annellated coumarins from 8-allylcoumarins

“…Allylation of phenols 16 furnished the RCM precursors 17 , which underwent the tandem RCM/allylic oxidation sequence to compounds 15 in fair yields (Table 5). All pyran-2-one-annellated coumarins 15 synthesized in the course of this study were previously described in the literature: compound 15a was used to investigate the regioselectivity of [2 + 2]-photocycloadditions [71], compound 15d was included in a comparative investigation into the fluorescence properties of 4-methylcoumarins [72], compounds 15b and 15c were tested for bacteriostatic activity [73] and insect-antifeedant activity [74], respectively. A common denominator of these reports is that a thorough investigation into the spectral and biological properties of these compounds is hampered by unsatisfactory yields and selectivities if classical coumarin syntheses are used.…”

“…A common denominator of these reports is that a thorough investigation into the spectral and biological properties of these compounds is hampered by unsatisfactory yields and selectivities if classical coumarin syntheses are used. Compound 15a , for instance, was obtained in only 14% yield from umbelliferone and malic acid in a Pechmann synthesis [71].…”

Synthesis and photochemistry of isothiocoumarins fused to an additional pyranone or thiopyranone ring

“…in furocoumarins or in corresponding benzodipyrandiones, induces a very high increase in efficiency in such reactions. 7, 8 Finally, the site-specific addition of either 13 or 16 to the thiinone C᎐ ᎐ C double bond of excited 4 is of interest, as "asymmetric" divinylbenzenes may exhibit such a selectivity, but sometimes random mixtures are obtained as well. 9 Here again more extensive studies are required in order for a better understanding of this behaviour.…”