Solution-phase switching

In one such TTF/DNP-based bistable [2]rotaxane 54+ (Fig. 8.6a), a long, rigid p-ter-phenyl spacer was employed between the TTF and DNP recognition sites and two tetraarylmethane stoppers were employed [22a] on both ends of the dumbbell component for the solution-phase switching studies. UV-Vis spectroscopy (Fig. 8.6b), which reveals the precise location of the CBPQT4+ ring on the dumbbell 

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Electrochemically Controlled Switching of TTF/DNP-based [2]Rotaxanes 8.4.2.1 Solution-phase Switching... 

In most cases, the overall synthesis time was greatly reduced (from hours or days to minutes) by switching from conventional to microwave heating, facilitating the rapid preparation of novel chemical entities. The combination of soUd-phase synthesis with microwave irradiation also allowed access to a few classes of molecules that had proven elusive via other synthetic strategies (traditional solution-phase synthesis). 

B. Linclau, A. K. Singh, D. P. Curran, Organic-Eluorous Phase Switches A Fluorous Amine Scavenger for Purification in Solution Phase Parallal Synthesis , J. Org. Chem 1999, 64, 2835. 

Phase-switching strategy was applied to the multistep synthesis of isoxazolines 45-47. The approach exploits the boronic acid functionality as a phase-tag which can be easily immobilized on diethanolaminomethyl polystyrene (DEAM-PS) resin and then released by treatment with wet THF. Each reaction step was carried out in solution and the products were purified by addition of the scavenging resin, followed by filtration, washing of the supported material, hydrolytic release and evaporation. Finally, the boronic acid could be used to introduce additional substituents on the molecule. For example, 46 was converted into the biaryl-containing isoxazoline 47 by a Suzuki cross-coupling reaction <07JCO193>. 

A efficient three-component solution-phase condensation of a 3-amino-5-alkylthio-1,2,4-triazoles with an aromatic aldehyde and an acetoacetamide was developed by Qiebanov and co-workers [100] for the rapid synthesis of 7-ary 1-2-alkylthio, 7-dihydro-1,2,4- triazolo[l,5-a]pyrimidine-6-carboxamides 54. All reactions were completed within 5 min of microwave irradiation at 120°C and provided the desired dihydroazolopyrimidines 54 in high yields and with excellent purities. The cyclocondensation reactions were performed in ethanol and a significant decrease of the product yield was observed when switching the solvent to acetic acid or DMF or when an acidic catalysts was added (Scheme 40). 

Linclau B, Sing AK, Curran DP. Organic-Fluorous phase switches a fluorous amine scavenger for purification in solution phase parallel synthesis. J Org Chem. 1999 64 2835-2842. Parlow JJ. Polymer-assisted solution-phase chemical library synthesis. Curr. Opin. Drug Discov. Devel. 2005 8 757-775. 

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