1,3-bis(diarylmethylidene)-2-methylidenecyclohexanes in cycloaddition and cyclodimerization reactions. The role of stereoelectronic factors.
Cycloaddition and cyclodimerization reactions of 1,3-dibenzylidene- and 1,3-bis(p-methoxybenzylidene)-2-methylidenecyclohexanes, i.e., the diaryltrienes with fixed S-cis-configurations of exocyclic double bonds are studied. These compounds undergo in situ cyclodimerization of the [4 + 2]-type upon dehydration of the precursor tertiary alcohols and form endo-adducts in the Diels-Alder reaction with N-phenylmaleimide. In the presence of CF3COOH, acid-catalyzed cyclodimerization takes place leading to methylidene-substituted spirocyclodimers, which undergo intramolecular cyclization upon prolonged contact with CF3COOH to form a fused carbocyclic system containing a central, 'three-petal' fragment of six-membered rings.
The behaviour of 2-methylene-3-ferrocenylmethylenecamphane under conditions leading to the cyclodimerization of ferrocenyl-1,3-butadienes
The behaviour of 2-methylene-3-ferrocenylmethylenecamphane under proton cyclodimerization conditions has been investigated. The stage involving the formation of the dimeric linear allylic cation has been confirmed in these interactions by isolating of corresponding diene. Its structure has been established unambiguously by X-ray methods. All substances isolated have been characterized by elemental analyses and 1H and 13C NMR spectral data.
“ PARTIALLY-ACTIVATED ” FLUX RESIDUE IMPACTS ON ELECTRONIC ASSEMBLY RELIABILITIES
The reliabilities of the flux residue of electronic assemblies and semiconductor packages are attracting more and more attention with the adoption of no-clean fluxes by majority of the industry. In recent years, the concern of “partiallyactivated” flux residue and their influence on reliability have been significantly raised due to the miniaturization along with high density design trend, selective soldering process adoption, and the expanded use of pallets in wave soldering process. When flux residue becomes trapped under low stand-off devices, pallets or unsoldered areas (e.g. selective process), it may contain unevaporated solvent, “live” activators and metal complex intermediates with different chemical composition and concentration levels depending on the thermal profiles. These partially-activated residues can directly impact the corrosion, surface insulation and electrochemical migration of the final assembly. In this study, a few application tests were developed internally to understand this issue. Two traditional liquid flux and two newly developed fluxes were selected to build up the basic models. The preliminary results also provide a scientific approach to design highly reliable products with the goal to minimize the reliability risk for the complex PCB designs and assembly processes.