Multistep Microwave-Assisted Synthesis of Avobenzone

Multistep synthesis is a key capstone experience in organic laboratory instruction. Here, a four-step synthesis of avobenzone, an active component in sunscreens, has been developed that can be completed in two 4 h laboratory periods. This synthesis incorporates green principles and includes an aldol condensation, electrophilic addition of bromine to an alkene, an E2 dehalogenation of a dibromide, and hydration of an alkyne. Highlights of this synthesis include the use of coupling constants to identify alkene configuration, NMR analysis to determine preferred tautomeric form, the use of microwave irradiation to reduce reaction times, a solvent-free synthesis of a chalcone, and a three-step reaction that can be completed in a single lab period.