## 1 Introduction  
Polysubstituted 2-aminothiophenes have shown to be versatile synthetic building blocks in the dye and other industries [1,2]. These useful compounds have also been significant with respect to their biological activity [3, 4, 5]. Due to their importance and versatility, the chemistry of 2-aminothiophenes has received much attention and several synthetic methods have been published [6, 7, 8]. Many of the methods reported involve difficult preparation of starting materials and multi-step synthesis. The most convenient method for preparing 2-aminothiophenes with a high degree of substitution is the Gewald reaction (Scheme 1) [9]. The Gewald method, involves the reaction of ketones, aldehydes or 1,3-dicarbonyl species with activated nitriles and elemental sulfur in the presence of an amine base. This method is an improvement over other existing routes for the synthesis of 2-aminothiophenes [10,11].  
Although the Gewald reaction possesses very good synthetic utility, there are three different variations which tailor the reaction for specific substrates. Of the three variations the second version of the Gewald reaction, which consists of a one-pot procedure, is the most efficient and straightforward. However, literature reports indicate aryl ketones show limited reactivity.  
**Scheme 1.** Three variations of the Gewald Reaction.  
Recently [PERSON], [PERSON] and co-workers developed a two-step, one-pot method for conducting the Gewald reaction with aryl ketones in high yield. In this version, sulfur is added in 3 portions, with the first portion being added after 3 h and subsequent additions of sulfur are needed over a period of 8-12 h [12]. The overall reaction time in this procedure is 36-40 h with isolated yields of 25%-70% of various 4-aryl-substituted 2-aminothiophene-3-carboxylates.  
Many modifications to the Gewald reaction have been developed including the use of solid support [13, 14, 15], microwave irradiation [16, 17], ionic liquids [18, 19], and with heterogeneous catalyst [20].  
Given the importance of this reaction in various industries, as well as in the building of combinatorial libraries, we wanted to develop a consistent one-step one-pot method for the Gewald reaction. We thought conducting this reaction via high speed ball milling (HSBM) would be less cumbersome and lead to a significant rate enhancement.  
HSBM is an environmentally benign method by which reagents are placed inside a vessel along with a ball-bearing that is shaken at high speeds in the absence of solvent [21, 22, 23]. The high speed attained by the ball-bearing has enough force to make an amorphous mixture of the reagents which in turn facilitates a chemical reaction. This method has been studied in metal alloying and for the generation of inorganic salts but this methodology is relatively new to organic synthesis.  
One of our research goals is focused on increasing the rate of multi-component reactions (MCR's). We recently demonstrated an increase in rate of the Baylis-Hillman reaction via HSBM conditions [24]. The success we had with the ball milled Baylis-Hillman reaction, coupled with our desire to obtain the polyfunctionalized Gewald products in a one-step, one-pot process, stimulated our interest towards the use of HSBM for this reaction. Because aryl ketones are known to react sluggishly in the Gewald reaction, we decided to use aryl ketones in our study of this reaction under ball milling conditions.