The photocycloaddition of dibenzoylmethanatoboron difluoride (DBMBF₂) with conjugated enones and en-esters

Abstract

YUAN L. CHOW, SHI-SEN WANG, and XIAN-EN CHENG. Can. J. Chem. 71, 846 (1993). Dibenzoylmethanatoboron difluoride (DBMBF,), the BF, complex of dibenzoylmethane, reacted from its singlet excited state with a,P-unsaturated ketones and esters to give 1,5-diketones by a [2+2] cycloaddition and ring-opening sequence in an analogous pathway to that observed in the photocycloaddition to olefins and dienes. The present photoreaction is unexpected since conjugated enones and en-esters are poor electron donors to comply with the previously proposed charge transfer requirement in DBMBF, photoreactions. The photocycloaddition to these substrates was highly regioselective and stereoselective, giving the head-to-head orientation, which could be enhanced by a-methyl substitution; P-methyl substitution increased the alternate head-to-tail orientation. The photolysis of a mixture of DBMBF, and a cyclic enone also caused the latter to dimerize to give head-to-head and head-to-tail dimers in significant yields. These photodimerizations were apparently caused by DBMBF, sensitization. The mechanism of the sensitization is discussed. [Traduit par la rCdaction1

Stereocomplexed Poly(lactic acid)−Poly(ethylene glycol) Nanoparticles with Dual-Emissive Boron Dyes for Tumor Accumulation

“…Additionally, a small shoulder at higher molecular weights can be seen in the UV signal of GPC traces of the older NP samples (see Supporting Information). This shoulder is most likely the result of BNP aggregation or possibly due to polymer cross-linking via peroxidation induced by PEG46 or photochemical reactions with the BF 2 dbm(I) dye 47, 48. It may be the case that freeze-drying of these NPs leads to crystallization of the PEG segments, which makes them difficult to redissolve in certain solvents such as water or THF, as was the case here.…”

“…This shoulder is most likely the result of BNP aggregation or possibly due to polymer cross-linking via peroxidation induced by PEG 46 or photochemical reactions with the BF 2 dbm(I) dye. 47,48 It may be the case that freezedrying of these NPs leads to crystallization of the PEG segments, which makes them difficult to redissolve in certain solvents such as water or THF, as was the case here. This is not an unlikely scenario, as aqueous solutions of proteins and suspensions of pegylated NPs are typically mixed with a lyoprotectant prior to freezedrying to prevent aggregation and allow for redistribution in water.…”

Role of Electron-Donating and Electron-Withdrawing Groups in Tuning the Optoelectronic Properties of Difluoroboron–Napthyridine Analogues

“…Excited states for all molecules show a dominant π → π* transition from HOMO to LUMO. The optical properties of these compounds were studied in DCM because these conditions do not result in boron–ligand dissociation or a photochemical reaction. , …”

“…The optical properties of these compounds were studied in DCM because these conditions do not result in boron−ligand dissociation 47 or a photochemical reaction. 48,49 3.4. Emission Spectra.…”

Synthesis and Photophysical Properties of Alkoxysilyl Derivatives of Dibenzoylmethanatoboron Difluoride

“…BF 2 bdks in their singlet‐excited state undergo photocycloaddition with alkenes and arenes; therefore, they can serve as starting compounds for the synthesis of 1,5‐diketones . BF 2 bdks are used in the design of a new polymethine dye with intense long‐wavelength absorption .…”