## 1 Introduction  
Solid-phase synthesis is a very attractive methodology for the time-efficient synthesis of diverse organic molecules [1; 2; 3; 4]. The initial step in the entire synthetic sequence is the selection of the appropriate linker for the immobilization of the first building block. The Wang linker [5] is the most commonly used acid-labile linker, and it has been used to immobilize carboxylic acids, alcohols, phenols, and amines [6; 7]. Typically, after finishing the synthesis, the product is released from the resin and the functional group that was initially used for immobilization will remain attached to the product. This functional group, referred to as the trace of the linker, may be an inherent part of the target molecules (peptides are the best examples), but for the synthesis of organic molecules that do not share a common functional group, the trace of the linker is undesirable. Therefore, numerous synthetic routes have been devised that enabled the synthesis to be performed in a traceless manner; heterocycles are undoubtedly the highly representative examples [8]. Here, we expand the application of Wang resin to the novel, traceless synthesis of ketones from acid-labile enol ethers, which were prepared via the Wittig reaction of resin-bound esters.  
Enol ethers represent valuable synthons in organic synthesis, and numerous methods for the synthesis of enol ethers have been reported; however, the Wittig olefination of esters is used rarely [9]. This 'nonclassical' Wittig reaction of carboxylate esters suffers from sluggish reactivity due to the low electrophilicity of the carbonyl carbon towards phosphoranes compared to the electrophilicity of aldehydes and ketones [10]. The reactions typically require the use of microwave irradiation (conventional heating reportedly did not yield any product) [11] or reactive phosphoranes such as cyanomethylentermethylphosphorane [12]. An alternative approach to enol ethers is the alkylidenation of ester carbonyls with metal carbene complexes [13] used, for example, in traceless solid-phase synthesis of indoles [14; 15].  
On the other hand, the intramolecular Wittig cyclization of phosphonium salt proceeded smoothly, and this reaction was successfully used by [PERSON] and [PERSON] in 1979 for the synthesis of dihydrofurans and dihydropyrans [16; 17], and later, this technique was used for the preparation of carbocycles [18; 19; 20] and heterocycles such as 2-alkylthiobenzimidazoles [21], indoles [22], 2-quinolones [23], and, recently, 4-alkoxy-1,5-dihydro-2\(H\)-pyrrol-2-ones [24; 25].  
Not surprisingly, although only a limited number of reports have described the application of enol ethers in the synthesis of ketones, the preparation of ketones from vinyl ethers using a Grignard reagent was reported in 1955 [26]. The hydrolysis of vinyl ethers has been studied on numerous occasions [27; 28; 29]; however, this technique has not been applied for general preparative use. Among the few recent reports in this area, silyl enol ethers were enantioselectivity converted to ketones by [PERSON] and coworkers [30; 31]. Ketones were prepared by the palladium-catalyzed regioselective aylation of vinyl ethers [32] and by the hydrolysis (MeOH/aq HCl, reflux) of vinyl ethers [33].  
To summarize the prior work, neither the synthesis of enol ethers via a Wittig olefination nor the use of enol ethers in the synthesis of ketones is a method of choice for ketone synthesis. Here, we report a simple and practical synthesis of acid-labile Wang resin-bound enol ethers via the Wittig olefination of carboxylate esters and subsequent acid-mediated traceless release of the ketones from the resin.