###### Abstract  
A reliable synthetic method based on the already known Blanc-Quelet methodology has been developed for upgrading bio-based phenols into valuable electrophilic mono-, di-, and trifunctional benzyl chlorides. These compounds show significant potential as building blocks for polymer production and the synthesis of specialty chemicals. As an example of their applicability, their direct interaction with formamide has been evaluated, obtaining an effective transformation towards the corresponding \(N\)-formylamides. These compounds represent versatile synthetic precursors to a variety of functionalized targets.  
biobased phenolics; Blanc-Quelet; benzyl chlorides; benzyl formamides 202  
expected to react efficiently with bio-sourced arenes. The reaction between aldehydes and phenolics is well established and frequently results in the coupling of two arene units, as the initial substitution product can further alkylate a second arene molecule. On this basis, phenolic resins or benzoxazines can be easily obtained by reaction with formaldehyde [5]. Moreover, other alkylants such as alkyl- or acyl-halides can transform phenolics into vinylic monomers by forming new ether or ester bonds with the phenolic oxygen atom, respectively. Epoxy monomers are also obtainable through interaction with epichlorohydrin, while polyurethanes can be prepared with isocyanates [5]. Some other specific processes such as bioconversion [8], continuous flow methods [9], or reductive catalytic technologies [10] have also been described.  
Going back to the interaction between phenolics and formaldehyde, it is interesting to note that the outcome of the process can be profoundly changed by the presence of chloride ions. First described by [PERSON] and [PERSON] in 1898 [11] and later expanded upon by [PERSON] [12], [PERSON] [13], and [PERSON] [14], this effect is attributed to a strong interaction between the halide and the aldehyde, leading to the formation of a chlorinated intermediate--such as a Cl,O-acetal [15]--which acts as the true electrophilic species in the reaction with the aromatic partner.  
Despite the long history of the Blanc-Quelet reaction [16], its application to bio-based phenols has been the subject of only a few studies [17]. In this work, we investigated the application of the Blanc-Quelet procedure for the selective chloromethylation of representative bio-based phenols, including vanillin, salicaldehyde, picool, eugenol, guaiacol, and \(p\)-cresol. The resulting benzyl halides (**2a**-**f**, Figure 1) serve as valuable building blocks for the production of bio-based materials and chemicals [18; 19; 20]. Diarylmethanes, novolac-, resol-, or reosol-type oligomers and resins are some of the valuable derivatives obtainable from benzyl chlorides.  
One interesting application of compounds **2a**-**f**, which exemplify an extension of their synthetic versatility, is their amidation to form benzyl formamides (**3a**-**f**, Figure 1). These molecular targets exhibit good potential as a source of many other functionalized building blocks and materials. Formamides are highly versatile intermediates, serving as precursors to a variety of functional groups and scaffolds. They can be converted into amines [21; 22; 23] or isocyanides [24; 25; 26] and may also be transformed into isocyanates [27], which in turn enable the synthesis of urethanes [28], ureas [29; 30], and thiocarbamates [31]. Additionally, specialized methods have been developed for coupling formamides with various synthons to generate valuable structures such as aminonitriles [32], tetrazoles [33], and lactams [34], which are often key structural motifs in low-molecular-weight active pharmaceutical ingredients.  
Figure 1: Upgrading of biobased phenols through the Blanc–Quelet reaction and amidation of chlorophyll derivatives (**2a**–**f**) to versatile formamides (**3a**–**f**).  
This synthetic approach represents a novel and practical strategy for upgrading bio-based phenols into valuable chemical building blocks.