A generally applicable synthesis of 1-aryl-2-(dimethylaminomethyl)prop-2-en-1-ones 2 involving reaction of aromatic methyl ketones 1 with paraformaldehyde and dimethylamine in dimethylformamide is described. The majority of experiments were conducted with these reagents, but the process can also be performed using dimethyl(methylene)ammonium chloride.Method A: (CH 2 O) n (3 equiv), Me 2 NH 2 Cl (2 equiv); Method B: CH 2 =NMe 2 Cl Scheme Downloaded by: York University libraries. Copyrighted material.

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The condensation of 1-aryl-2-dimethylaminomethylprop-2-en-1-ones 4 with 2-aminopyridines 5 gives rise to the 3-benzoyl-3,4-dihydro-2H-pyrido[1,2-a]pyrimidines 3. The reaction is initiated by addition of the pyridine amino group to the enone double bond, followed by deamination and ring closure to give the anellated pyrimidine ring system, which is an excellent precursor for the synthesis of pharmacological active compounds.A number of biologically active compounds including antiallergic, 1,2 analgetic, 3,4 antihyperlipidemic, 5 neuroleptic, 6,7 antihistaminic, 8 and antihypertensic 9 agents are 3-substituted pyrido[1,2-a]pyrimidines, some of them hydrogenated at the pyridine nucleus ( Figure 1). The most common method for their preparation is either the condensation of 2-aminopyridines with ethoxymethylene malonic acid derivatives or the ring closure reaction of N-(2-pyridyl)-aminomethylenemalonic acid derivatives obtained in good yields by heating 2-aminopyridines with active methylene compounds in the presence of orthoformates. 10-16 Thus, a typical procedure is the condensation of 2-amino-6-methylpyridine with ethoxymethylene malonic acid ester (EMME) to the respective hetarylaminoacrylic acid ester followed by cyclization using a mixture of phosphoryl chloride and polyphosphoric acid. 4,17 Reagents such as EMME possess three electrophilic centers, whose condensation with ambifunctional nucleophilic compounds in one or two steps generally gives rise to the formation of 3-substituted aromatic heterocycles 3, unsubstituted in 2-position. Figure 1We found a simple procedure for preparing 3-substituted pyrido[1,2-a]pyrimidines by condensation of 2-aminopyridines 5 with enone Mannich bases 4, which are easily accessible through heating of aryl methyl ketones, paraformaldehyde, and N,N-dimethylamine hydrochloride in DMF. 18 Like EMME, these enone Mannich bases 4 are characterized by three electrophilic centers. After addition of the nucleophile the dimethylamino group is eliminated and therefore renders possible ring closure reaction to form anellated heterocycles 3. We performed the cyclizations of 4 with 2-aminopyridines 5 in a refluxing ethanol/water mixture (1: 1) in order to study the influence of the polyfunctional character of both reactants. 19 Scheme 1Isolation of the resulting products as hydroperchlorates showed that -as anticipated -an addition-elimination mechanism had taken place. In the first step, the 2-aminopyridine 5 adds to the double bond affording the saturated intermediates 6. 20 Next, the third electrophilic center is generated by elimination of Me 2 NH 2 Cl to form the enone 7 followed by a second addition reaction to the ring closed heterocycle 3, partly hydrogenated in the pyrimidine moiety. The intermediates 6 and 7 could not be isolated. Obviously, attack at the keto carbonyl group of the enone Mannich base 4 by the 2-aminopyridine 5 with formation of the corresponding azomethine derivatives does not occur, the conceivable follow-up products 8 or 9 were not found ( Figure 2). When perform...

Abstract:For brittle fracture behaviour of carbon fibre reinforced plastics (CFRP) under compression, several approaches exist, which describe different mechanisms during failure, especially at stress intensifications. The failure process is not only initiated by the buckling fibres, but a shear driven fibre compressive failure beneficiaries or initiates the formation of fibres into a kink-band. Starting from this kink-band further damage can be detected, which leads to the final failure. The subject of this work is an experimental investigation on the influence of ply thickness and stacking sequence in quasi-isotropic CFRP laminates containing stress intensifications under compression loading. Different effects that influence the compression failure and the role the stacking sequence has on damage development and the resulting compressive strength are identified and discussed. The influence of stress intensifications is investigated in detail at a hole in open hole compression (OHC) tests. A proposed interrupted test approach allows identifying the mechanisms of damage initiation and propagation from the free edge of the hole by causing a distinct damage state and examine it at a precise instant of time during fracture process. Compression after impact (CAI) tests are executed in order to compare the OHC results to a different type of stress intensifications. Unnotched compression tests are carried out for comparison as a reference. With this approach, a more detailed description of the failure mechanisms during the sudden compression failure of CFRP is achieved. By microscopic examination of single plies from various specimens, the different effects that influence the compression failure are identified. First damage of fibres occurs always in 0°-ply. Fibre shear failure leads to local microbuckling and the formation and growth of a kink-band as final failure mechanisms. The formation of a kink-band and finally steady state kinking is shifted to higher compressive strains with decreasing ply thickness. Final failure mode in laminates with stress intensification depends on ply thickness. In thick or inner plies, damage initiates as shear failure and fibre buckling into the drilled hole. The kink-band orientation angle is changing with increasing strain. In outer or thin plies shear failure of single fibres is observed as first damage and the kink-band orientation angle is constant until final failure. Decreasing ply thickness increases the unnotched compressive strength. When stress intensifications are present, the position of the 0°-layer is critical for stability under compression and is thus more important than the ply thickness. Central 0°-layers show best results for OHC and CAI strength due to higher bending stiffness and better supporting effect of the adjacent layers.