A novel photocatalysis to construct the 3-acyl-4-arylcoumarin framework from simple aldehyde with ynoate is described. The reaction proceeded through an acyl radical intermediate generated by hydrogen atom abstraction from aldehyde, followed by reaction with ynoate and then cyclization to afford coumarins. This valuable radical cyclization reaction gave over 20 coumarin derivatives in moderate to good yields with inexpensive 2-tBu-anthraquinone as a catalyst. In addition, synthetic coumarins were investigated for 5α-dihydrotestosterone (DHT)-induced secretion of prostate-specific antigen (PSA) levels and cell proliferation of androgen-dependent CWR22Rv1 cells.