br Materials and methods br Results and discussion br Conclusion

Materials and methods

Results and discussion

Conclusion
This study confirms to some extent the expected behavior for ultrasonic transducers with frequencies of 400kHz and 2MHz in terms of their penetrative distance in fluids and acoustic pressure distribution when working with large geometries up to 2m in length. Ultrasound with a frequency of 400kHz was capable of penetrating through almost the entire length of the vessel, and still produced a uniform sound pressure distribution with normalized pressures exceeding 60%. By contrast, high frequency ultrasound at 2MHz, displayed sharp decline in active sound pressure within the first 200mm from the surface of the transducer. However, 2MHz ultrasound was able to be rendered more uniform in sound pressure magnitude (with magnitudes exceeding 60%) by placement of a stainless steel reflector plate within 500mm of the transducer surface.
For long distance sonoprocessing, it Tyrosine Kinase Inhibitor Library is advantageous to use lower frequency ultrasound since sound pressure is more uniformly distributed with distance. For Tyrosine Kinase Inhibitor Library applications requiring high frequency ultrasound greater than 2MHz, shorter operating distances with placement of reflector plates, would enable more uniform sound pressure. The sound pressure distributions mapped in this study provides a guide for reactor designs that will have industrial relevance to sonoprocessing and sonochemistry applications using high frequency ultrasound.

Acknowledgments
The authors would like to acknowledge the RMIT University final year research program for establishment of Michael Coventry’s studentship at CSIRO.

Introduction
Ferrocene was discovered in 1951 [1], and immediately attracted research attention thanks to its peculiar structure, chemical and thermal stability, redox properties and the biological compatibility of some ferrocenyl derivatives. An intense and lively debate on the nature of this milestone in the history of organometallic chemistry has continued since its first synthesis. Ferrocenyl based ligands have found successful applications in metal catalysis [2,3], even in large scale applications for the industrial synthesis of optically active compounds [4]. Several biological functions for ferrocene and its derivatives have been reported [5,6] as well as antitumor activity [7]. The ferrocene moiety has also found interesting uses in material science [8,9]. It is evident that the design of simple and efficient synthetic protocols for ferrocenyl derivatives and the use of multicomponent reactions (MCR) is a promising strategy [10,11].
A number of the Authors have recently and successfully dedicated study to MCRs by setting up a one-pot domino reaction that combines the allylindation of 1H-indole-3-carbaldehyde with dehydrative alkylation by C and N nucleophiles [12]. This methodology exploits the Barbier-type indium-mediated allylation of aldehydes, which was discovered in 1988 by Butsugan and co-workers [13], and which has been developed over the years to give general and efficient stereoselective protocols [14]. The alcohol formed as a result of the Barbier allylation is driven to in situ dehydratation-Friedel–Crafts alkylation [15], due to the presence of a Lewis acid (InIII species, arising from the allylindation) in the reaction mixture.
Similar synthetic protocols, using metals or organometallic reagents, have been successfully carried out under ultrasound (US) irradiation. In 2006, Lee et al. described the advantages of sonochemical conditions in the indium mediated Reformatsky reaction [16]. The use of US allows mild reaction conditions to be used, generally reduces reaction time and affords high yields. More recently, a comprehensive literature survey has shown the beneficial effect of US in a classical coupling promoted by zero-valent metal species in heterogeneous mixtures [17].
In this piece of work, we successfully extend the domino allylindation–alkylation MCR protocol to ferrocenecarboxaldehyde 1 with a variety of nucleophiles 2a–r (Scheme 1). Ultrasonic irradiation proved to be crucial for the transformation and a library of unknown derivatives 3a–r have been synthesized in satisfactory to good yields.