Solid State Photochemistry of Isocoumarins and Isothiocoumarins

Development of Fluorescent Isocoumarin-Fused Oxacyclononyne - 1,2,3-Triazole Pairs

Fluorescent isocoumarin-fused cycloalkynes, which are reactive in SPAAC and give fluorescent triazoles regardless of the azide nature, have been developed. The key structural feature that converts the non-fluorescent cycloalkyne/triazole pair to its fluorescent counterpart is the pi-acceptor group (COOMe, CN) at the C6 position of the isocoumarin ring. The design of the fluorescent cycloalkyne/triazole pairs is based on the theoretical study of the S1 state deactivation mechanism of the non-fluorescent isocoumarin-fused cycloalkyne IC9O using multi-configurational ab initio and DFT methodologies. The calculations revealed that deactivation proceeds through the electrocyclic ring opening of the α-pyrone cycle and is accompanied by a redistribution of electron density in the fused benzene ring. We proposed that the S1 excited state deactivation barrier could be increased by introducing a pi-acceptor group into a position that is in direct conjugation with the formed C=O group and has a reduced electron density in the transition state. As a proof of concept, we designed and synthesized two fluorescent isocoumarin-fused cycloalkynes IC9O-COOMe and IC9O-CN bearing pi-acceptors at the C6 position. The importance of the nature of a pi-acceptor group was shown by the example of much less fluorescent CF3 -substituted cycloalkyne IC9O-CF3 .

Base-promoted thioannulation of o-alkynyl oxime ethers with sodium sulfide for the general synthesis of isothiocoumarins

A general and efficient strategy for the one-pot synthesis of isothiocoumarin-1-ones has been developed via the base-promoted 6-endo-dig thioannulation of o-alkynyl oxime ethers using the cheap and readily available Na₂S as the sulfur source. Mechanistic studies disclosed that the reaction proceeded through two C-S bond formations, N-O bond cleavage and the final hydrolysis of imines.

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

The [2 + 2] photocycloaddition is undisputedly the most important and most frequently used photochemical reaction. In this review, it is attempted to cover all recent aspects of [2 + 2] photocycloaddition chemistry with an emphasis on synthetically relevant, regio-, and stereoselective reactions. The review aims to comprehensively discuss relevant work, which was done in the field in the last 20 years (i.e., from 1995 to 2015). Organization of the data follows a subdivision according to mechanism and substrate classes. Cu(I) and PET (photoinduced electron transfer) catalysis are treated separately in sections 2 and 4 , whereas the vast majority of photocycloaddition reactions which occur by direct excitation or sensitization are divided within section 3 into individual subsections according to the photochemically excited olefin.

An expeditious and environmentally friendly synthesis of 3-substituted isocoumarins using microwave irradiation

A microwave-assisted, environmentally friendly, high-yielding, time-saving synthesis of medicinally important 3-substituted isocoumarins was carried out in a single step by direct condensation of homophthalic acid with aryol and acyl chlorides under solvent-free conditions without any solid support. The synthesised isocoumarins were structurally characterised by microanalysis, 1H NMR, EI, IR and UV.

Amicoumacin antibiotic production and genetic diversity of Bacillus subtilis strains isolated from different habitats

One of the most interesting groups of phenolic compounds is comprised of the low molecular weight phenylpropanol derivative substances named isocoumarins, which possess important biological activities. In this study, the isocoumarin production and genetic diversity of 51 Bacillus strains isolated from different geographical and ecological niches were studied. Using molecular identification techniques, 47 strains were identified as B. subtilis, three as B. licheniformis and one as B. pumilus. When these strains were screened for isocumarin production, 11 belonging to the species B. subtilis produced amicoumacins, antibiotics of the isocoumarin group. RAPD analysis demonstrated that these strains fell into two groups which contained only these amicoumacin producers. No association was detected between RAPD profiles and the geographic origin or habitat of the strains tested. In conclusion, production of amicoumacin antibiotics by B. subtilis is a common characteristic of individual strains that presented genetic and physiological homogeneity.

Photochemical synthesis of aldehydes in the solid phase

A substituted anthraquinone (AQ), previously shown to photochemically generate benzaldehyde in methanol solution, was attached to a commercially available resin via an 11 carbon tether and an amide bond. Photolysis of the polymer-bound AQ with visible or 350 nm UV light resulted in the formation of benzaldehyde in yields of 50-55% as determined by HPLC. The phenolic positions in the polymer were then alkylated using benzyl bromide and 1-iodo-3-(4-nitrophenyl)propane in a coupling reaction with K(2)CO(3) as a base and a solution-phase proton shuttle. Photolysis of these alkylated polymers resulted in the formation of benzaldehyde (54-89%) and 3-(4-nitrophenyl)-propanal (58-67%). The yields of both aldehydes dropped considerably with subsequent realkylation and photolysis, and the polymer beads began to show signs of deterioration. This is the first time that aldehydes have been made photochemically on a solid-supported phase.

Photochemistry of 4H,7H-Benzo

The title compound 1 was synthesized starting from 1, 2-bis(2-hydroxyethyl)benzene (2). Irradiation (350 nm) of 1 in CH(3)CN affords the all-cis-dimer 6 in >90% yield. Irradiation (>390 nm) of 1 in the presence of tetrachloroethene leads selectively to the monocyclobuta adduct 8, which on subsequent irradiation is converted to a 4:1 mixture of biscyclobuta derivatives 9 and 10.