Phenylpropanoids are the most common types of natural products and have a wide range of important functions in plants, e.g. as structural components (such as lignin). In particular, monolignols are plant-derived aromatic compounds with many potential applications. Even though monolignols are present in high amounts in lignin, its depolymerization and the isolation of the individual monolignols is difficult due to its complex and highly crosslinked structure. In this work, a route for the preparation of various methylated and hydroxylated cinnamaldehyde and cinnamyl alcohol derivatives was developed, starting from their corresponding acids. On the one hand, a flavin-dependent monooxygenase from E. coli was optimized by rational design for hydroxylation of bulky substrates. On the other hand, a system consisting of two enzymes could be replaced by an enzyme with two domains. Furthermore, a cell-free modular system for the synthesis of phenylpropanoids was developed. As an example, the synthesis of vanillin was constructed in vitro. A set of eight enzymes was used for a continuous conversion of p-coumaric acid to vanillin.