Catalytic synthesis of anti-uv and antioxidant conjugated 8-8 dimers in a green solvent

A process for preparing a dimer of formula (II), (III) or (IV):

• obtained by reduction of dimer of formula (I):
• wherein:
• R2 and R3 are independently selected from a linear, cyclic or branched C1 to C8 alkyl group or a linear, cyclic or branched C1 to C8 O-alkyl group:
• R4 is an H, a linear, cyclic or branched C1 to C30 alkyl group, or an organic (mono- or di-)acid hydro group;
• R6 is an H, an acetyl group or a linear, cyclic or branched C1 to C8 alkyl group, a silyl, benzyl or benzoyl protecting group;
• X is a C═O group, a CO2 group or a C(O)NR5 group, wherein R5 is an H or a linear, cyclic or branched C1 to C8 alkyl group.

A compound of formula (I′)

• wherein:
• R2 and R3 are an OMe group;
• R4 is a linear, cyclic or branched C1 to C30 alkyl group or an organic (mono- or di-)acid hydro group;
• R6 is an H, an acetyl group or a linear, cyclic or branched C1 to C8 alkyl group, a silyl, benzyl or benzoyl protecting group;
• X is an O, an NR5 group wherein R5 is an H or a linear, cyclic or branched C1 to C8 alkyl group;
• with the exception of the sinapate ester dimers corresponding to the following CAS numbers:
• 156257715-4, 1402923-23-2, 1402923-16-3, 1338096-56-2, 1026918-37-5, 915770-86-4, 852713-63-4, 683204-87-7, 389569-68-0, 73119-38-7, 56136-42-6, 53136-39-1, 56136-37-9 and the sinapate amide dimer corresponding to CAS number 88865-57-0.