Regio- and stereoselective ring-opening reactions of cyclopropenones. α-methylene-γ-butyrolactones via additions of trichlorocyclopropenylium ions to alkenes

The 2-chloro-3-(2′-chloroalkyl)cyclopropenones 4, readily obtained by hydrolysis of the adducts of the trichlorocyclopropenylium ion onto alkenes, thermally rearrange to propiolic acid chlorides 6. Treatment of 4 with TosOH·H2O in CH2Cl2 yields the (E)-3-chloro-2-(2′-chloroalkyl)acrylic acids 9, which have been converted in two simple steps to -methylene-γ-butyrolactones 11 with good overall yields

Addition reactions of the trichlorocyclopropenylium ion with alkenes. A novel access to cyclopropene and cyclopropenone derivatives

Trichlorocyclopropenylium tetrachloroaluminate 1+-AlCl−4 reacts with alkenes in nitromethane at −35°C to give the 1:1 addition products 2+-AlCl−4, which can be converted into the 2-chlorocyclopropenones 5 or the ä,β-acetylenic carboxylates 6

4,5,12,13-Tetrabromo[2.2]paracyclophane - A New Bis(aryne) Equivalent

The reaction of 2 with nBuLi at -78°C generates aryne intermediates within the aromatic rings of [2.2]paracyclophane which are trapped in Diels-Alder reactions with dienes like furan, 1,9-diphenylisobenzofuran, or cyclopentadiene. Reductive deoxygenation with low-valent titanium reagents or TMSI converts the adducts of furan and isobenzofuran into anti-[2.2]paracyclophanes 4 and 5, respectively. The reaction of two aryne intermediates with [2.2](2,5)furanophane (7) yields 8 with three [2.2]paracyclophane units arranged in a stair-like fashion; yet, in this compound the highly shielded oxygen atoms cannot be removed anymore by reduction

Limited efficacy of forward contact tracing in epidemics

Infectious diseases that spread silently through asymptomatic or pre-symptomatic infections represent a challenge for policy makers. A traditional way of achieving isolation of silent infectors from the community is through forward contact tracing, aiming at identifying individuals that might have been infected by a known infected person. In this work we investigate how efficient this measure is in preventing a disease from becoming endemic. We introduce an SIS-based compartmental model where symptomatic individuals may self-isolate and trigger a contact tracing process aimed at quarantining asymptomatic infected individuals. Imperfect adherence and delays affect both measures. We derive the epidemic threshold analytically and find that contact tracing alone can only lead to a very limited increase of the threshold. We quantify the effect of imperfect adherence and the impact of incentivizing asymptomatic and symptomatic populations to adhere to isolation. Our analytical results are confirmed by simulations on complex networks and by the numerical analysis of a much more complex model incorporating more realistic in-host disease progression

Synthesis and Diels-Alder Reactions of 1,2-Dimethylene- and 1,2,9,10-Tetramethylene-[2.2]paracyclophane: New Routes to Bridge-Anellated[2.2]Paracyclophanedienes

The title compounds 8 and 1 have been synthesized in three steps each from 1,2-dibromo[2.2]paracyclophan-1-ene (2) and 1,2,9,10-tetrabromo[2.2]paracyclophane-1,9-diene (4), respectively. Copper-mediated coupling of vinyl bromides 2 and 4 with methyl- and phenylmagnesium bromide gives substituted [2.2]paracyclophanes 3-CH3, 3-Ph, 5-CH3, and 5-Ph in good yields. The high reactivity of the [2.2]paracyclophane-1,2-dimethylene moieties in 8 and 1 in Diels-Alder reactions has been verified in cycloadditions with p-benzoquinone to give 10 and 13 and with naphthalene 1,4-endoxide to yield 12

[2.2](4,7)Isobenzofuranophanes - Synthesis, Characterisation and Reactivity

The isomeric Diels-Alder adducts 3, obtained by cycloaddition of tetraphenylcyclopentadienone to the 4,5:12,13-bis-(oxanorbornadieno)[2.2]paracyclophanes syn,syn- and anti,-syn-2[Note ][The stereochemical descriptors syn and anti refer to the orientation of the oxygen bridge in the oxabicyclo[2.2.1]heptadiene subunits with respect to the [2.2]paracyclophaneskeleton.], yield the unstable isobenzofuranophane 4 by consecutive extrusion of carbon monoxide and tetraphenylbenzene when heated to 180°C. The molecular ion of 4 was observed in the EI mass spectrum. The stable tetraphenyl-substituted analogue 10 was synthesized independently from the previously unknown 4,5,12,13-tetrabenzoyl[2.2]paracyclophane (9). UV/Vis as well as fluorescence spectra and an X-ray crystal structure analysis of 9 are reported

Hydrogen adsorption on and desorption from Si: Considerations on the applicability of detailed balance

The translational energy of D2 desorbed from Si(100) and Si(111) surfaces was measured and found roughly equal to the thermal expectation at the surface temperature Ts. Combining these results with previously measured internal state distributions, the total energy of the desorbed molecules is approximately equal to the equilibrium expectation at Ts. Thus adsorption experiments, which suggest a large energetic barrier, are at variance with desorption experiments, which exhibit a trivial adsorption barrier, and the applicability of detailed balance for this system needs to be reexamined