This allowed us to utilize our telescoped flow strategy (as shown in Scheme 2) for electronpoor aldehydes and, to our delight, similar results were obtained as with the fed-batch procedure (see e.g., 28, 29, 35-37). Notably, different classes of hydrogen donors, such as hydrocarbons (39, 43%), (thio)ethers (40-41, 47-68%), protected amines (42, 51%) and amides (43, 55%), proved all competent reaction partners. In all cases, the reaction performed particularly well, delivering densely functionalized alkenes in high yields and Estereoselectively. It is important to note that it would be extremely challenging to access either of these with the current radical allylation methodologies, which do not allow to synthesize trisubstituted alkenes (Scheme 1D). Unfortunately, all attempts to install fully-substituted olefins, by engaging ketones in the HWE step, failed. Interestingly, our protocol was also amenable to aliphatic aldehydes containing enolizable positions (44-48, 57-71% yield). The use of protected piperidine-4-carboxaldehyde allowed to obtain the corresponding allylated products 47 and 48 in excellent yields (60-68 %) and with good diastereomeric ratios. As a testament to the power of this strategy to rapidly diversify double bonds, medicinal agents and natural products containing carbonyls, such as acetyl-protected helicin, citronellal and indomethacin aldehyde derivatives, were also reactive delivering the targeted value-added olefins in synthetically useful yields (49-51, 20-63%). The regioselective and late-stage installation of allyl groups opens up innumerable possibilities for further diversification. As an illustration of this synthetic potential, we explored diverse conditions for the conversion of synthon 4 into functionalized derivatives (Scheme 4). The olefin and the ester functionalities could be orthogonally reduced by exploiting different reduction conditions, yielding compounds 52 (70%) and 53 (62%), respectively. Moreover, compound 4 was an ideal substrate for another Giese-type radical addition using decatungstatephotocatalyzed HAT (54, 62%). Finally, product 55 could be obtained via a classical Mizoroki-Heck-type coupling (60%). 58 In conclusion, we have developed a practical methodology which enables the modular and regioselective allylation of C(sp 3 )-H bonds. Our strategy involves a synergistic merger of a photocatalytic Hydrogen Atom Transfer and an ensuing Horner-Wadsworth-Emmons olefination in a scalable and telescoped flow protocol. In its present form, the synthetic platform offers rapid access to various di-and tri-substituted olefins from abundantly available hydrocarbon feedstocks, including biologically active molecules. The operational simplicity of our flow protocol, requiring no intermediate purification, should facilitate a rapid transition from academic to industrial settings. We anticipate that this practical method will unlock new synthetic opportunities for the rapid and late-stage diversification of building blocks, medicines, natural products and other specialty chemicals.