Flow photochemistry: Old light through new windows

• Jonathan P. Knowles,
• Luke D. Elliott and
• Kevin I. Booker-Milburn

Beilstein J. Org. Chem. 2012, 8, 2025–2052, doi:10.3762/bjoc.8.229

• the lower-power light source. These longer residence times further lowered the reactor productivity to 0.15 mmol/h [24]. Photooxygenations Direct oxygenation of organic molecules through the photosensitised addition of singlet oxygen represents an atom-economic method of functionalisation and is

• of bulk solutions, which combined with the extremely short lifetime of singlet oxygen means that lengthy irradiations are often required. These issues can be overcome through the use of continuous-flow chemistry: reactions performed in this manner have only a small amount of oxygenated solvent and

• peroxide product present at any one time, and this can be reduced immediately upon leaving the reactor. The smaller reactor volumes involved in flow chemistry also mean that irradiation is efficient and hence that the singlet oxygen generated can react within its short lifetime. Falling-film microreactors

The chemistry of bisallenes

• Henning Hopf and
• Georgios Markopoulos

Beilstein J. Org. Chem. 2012, 8, 1936–1998, doi:10.3762/bjoc.8.225

Triple-channel microreactor for biphasic gas–liquid reactions: Photosensitized oxygenations

• Ram Awatar Maurya,
• Chan Pil Park and
• Dong-Pyo Kim

Beilstein J. Org. Chem. 2011, 7, 1158–1163, doi:10.3762/bjoc.7.134

• oxygenations of α-terpinene, citronellol, and allyl alcohols. Keywords: gas–liquid reaction; microreactor; photosensitization; singlet oxygen; Introduction Microreactors have recently attracted much interest among the scientific community for performing laboratory operations on small scales [1][2][3][4][5][6

• from long reaction times due to restricted spatial illumination. In addition, the short lifetime of singlet oxygen in solutions, the low interfacial area between the oxygen and the reaction solution, and the long molecular diffusion distances significantly reduce the reaction efficiency. In this

Fine-tuning alkyne cycloadditions: Insights into photochemistry responsible for the double-strand DNA cleavage via structural perturbations in diaryl alkyne conjugates

• Wang-Yong Yang,
• Samantha A. Marrone,
• Nalisha Minors,
• Diego A. R. Zorio and
• Igor V. Alabugin

Beilstein J. Org. Chem. 2011, 7, 813–823, doi:10.3762/bjoc.7.93

• acetamides. The significant protecting effect of the hydroxyl radical and singlet oxygen scavengers to DNA cleavage was shown only with m-lysine conjugate. All three isomeric lysine conjugates inhibited human melanoma cell growth under photoactivation: The p-conjugate had the lowest CC50 (50% cell

• previous mechanistic studies suggested that neither singlet oxygen nor diffusing oxygen- and carbon-centered radical species play a significant role under the conditions where the most efficient ds cleavage by monoalkynes is observed (pH 6) [25]. From the narrowed list of mechanistic scenarios, base

• on DNA cleavage In order to get further insight into the mechanism of the DNA cleavage by the three conjugates, we used the plasmid relaxation assays for the cleavage with conjugates 1, 6, and 7 in the presence of hydroxyl radicals (glycerol, DMSO) and singlet oxygen (NaN3) scavengers [65]. The

Palladium-catalyzed formation of oxazolidinones from biscarbamates: a mechanistic study

• Benan Kilbas and
• Metin Balci

Beilstein J. Org. Chem. 2011, 7, 246–253, doi:10.3762/bjoc.7.33

• nucleophile is not necessary to form oxazolidinones. The metal is probably bonded to the allylic system from the same face as the nucleophile. Keywords: bicyclic endoperoxides; biscarbamates; oxazolidinone; Pd-catalyzed allylic reaction; singlet oxygen; Introduction Palladium-catalyzed carbon–carbon bond

• shift the equilibrium to the norcaradiene 4b side, while electron donating substituents, such as –OR, –NR2 favor the cycloheptatriene 4a structure. It has been shown that singlet oxygen and 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD) are sufficiently reactive to intervene in the cycloheptatriene

Synthesis of spiroannulated and 3-arylated 1,2,4-trioxanes from mesitylol and methyl 4-hydroxytiglate by photooxygenation and peroxyacetalization

• Axel G. Griesbeck,
• Lars-Oliver Höinck and
• Jörg M. Neudörfl

Beilstein J. Org. Chem. 2010, 6, No. 61, doi:10.3762/bjoc.6.61

• -hydroperoxy homoallylic alcohols (prepared by the ene reaction of the allylic alcohols mesitylol and methyl 4-hydroxytiglate, respectively, with singlet oxygen) to give spiroannulated 1,2,4-trioxanes 5a–5e and 9a–9e, respectively. A second series of 3-arylated trioxanes 10a–10h, that are available from the

• hydroperoxy alcohol 4 and benzaldehyde derivatives, was investigated by X-ray crystallography. Keywords: ene reaction; peracetalization; peroxides; singlet oxygen; trioxanes; Introduction The antimalaria-active molecule artemisinin (1) is a naturally occurring sesquiterpene peroxide with remarkable

• singlet oxygen ene reaction of allylic alcohols as a route to ß-hydroperoxy alcohols that can be transformed into 1,2,4-trioxanes by reaction with carbonyl compounds in the presence of Lewis acids [11]. This approach leads to simple cyclic peroxides (e.g. 2) which in some cases show similar antimalarial

Synthesis of a new class of aminocyclitol analogues with the conduramine D-2 configuration

• Latif Kelebekli,
• Yunus Kara and
• Murat Celik

Beilstein J. Org. Chem. 2010, 6, No. 15, doi:10.3762/bjoc.6.15

• cyclooctatetraene (8) by the addition of mercury(II) acetate [31]. Tetraphenylporphyrin sensitized photooxygenation of diacetoxydiene 9 with singlet oxygen gave the expected endoperoxide 10. Reduction of the peroxide bond in 10 was performed with thiourea under very mild conditions to give the cis-diol 11 in 99

• -dichlorobicylooctadiene 19 with singlet oxygen gave the expected endoperoxide 20 [19][20][21] (Scheme 4). Since the dichlorobicyclooctadiene 19 has no plane of symmetry, singlet oxygen approaches the diene unit exclusively from the less crowded side of the molecule in accord with previous reports [20][21]. Reduction of

Sordarin, an antifungal agent with a unique mode of action

• Huan Liang

Beilstein J. Org. Chem. 2008, 4, No. 31, doi:10.3762/bjoc.4.31

• al. [20]. The resultant alcohol was converted to the methyl ether using NaH and MeI. The subsequent Cope rearrangement of 10 occurred at 200 °C via a boat-like transition state [18] to yield 11. The elaboration of this material to 12 involved treatment with singlet oxygen and AcCl [21] to yield α,β