Some 5-alkyl- and 5-alkenyl-resorcinols were synthesised from commercially available 3,5-bis(benzyloxy)benzaldehyde by ultrasound-assisted Wittig reaction with alkyltriphenyl phosphonium bromides in basic aqueous condition, followed by debenzylation and simultaneously reduction of a double bond of the styrene type with Na/n-BuOH in overall yields of 62–72%.