Synthesis of Substituted Stilbenes via Direct Decarboxylative Coupling of Cinnamic Acids with Arylboronic Acids under Palladium Catalysis

Abstract

Readily available cinnamic acids possessing a hydroxy group including ferulic acid efficiently undergo direct decarboxylative arylation under palladium catalysis to form hydroxylated stilbenes. The reaction of related acids is also described.

Selective Depolymerisation of γ‐Oxidised Lignin via NHC Catalysed Redox Esterification

“…To highlight the potential value further a selection of interesting transformations reported in the literature involving 5 b are also summarised in Scheme . For example, NHC‐catalysed decarboxylation of 5 b gives 4‐vinylsyringol 6 (Scheme (reaction c)) a potent antimutagenic compound, whilst palladium catalysed decarboxylative coupling with arylboronic acids gives stilbenes such as 7 (Scheme (reaction d)) . 5 b can also serve as the starting point for the synthesis of more complex molecules such as the potential antioxidant dimer 8 and structures 9 and 10 …”

“… Conversion of selected lignin depolymerisation products to cinnamate‐type esters and acids and examples of literature conversions of sinapic acid ( 5 b ). Reaction conditions: This work: a) MsOH, d 8 ‐toluene, 90 °C, 10 min, 93 % ( 4 a ), 91 % ( 4 b ); b) KO t Bu, i ‐PrOH, 120 °C, 24 h, 96 % ( 5 a ), 94 % ( 5 b ); Literature reports using 5 b : c) 1‐Ethyl‐3‐methyl imidazolium acetate, DMSO, 100 °C, 60 min, 100 %; d) Phenylboronic acid, Pd(acac) 2 , Cu(OAc) 2 , LiOAc, DMF, 60 °C, 8 h, 89 %; e) (i): HCl, EtOH, reflux, 2d; (ii): H 2 , Pd/C, EtOAc, 10 °C, 45 min; (iii) 1,4‐Butanediol, CAL−B, 75 °C, 4–72 h, 87 %; f) (i): Horseradish peroxidase−H 2 O 2 , aq. acetone; (ii) acetic anhydride/pyridine; (iii) bromine, NH 4 OAc, AcOH, 50 °C, 6 h; (iv) AcCl−MeOH, 16 h; (v) Pd/C−Et 3 N, H 2 , MeOH, 2d, 80 %; (vi) DIBAL−H, toluene, 2 h; (vii) pyrrolidine, 3 min; g) (i) FeCl 3 , EtOH, RT., 1 h; (ii) 1 N NaOH, RT., 5 min, 62 % …”

“…For example, NHC-catalysed decarboxylation of 5 b gives 4-vinylsyringol 6 (Scheme 3 (reaction c)) a potent antimutagenic compound, [29,30] whilst palladium catalysed decarboxylative coupling with arylboronic acids gives stilbenes such as 7 (Scheme 3 (reaction d)). [31] 5 b can also serve as the starting point for the synthesis of more complex molecules such as the potential antioxidant dimer 8 and structures 9 and 10. [32][33][34] In summary, several different elegant methods have previously been reported for the selective oxidation and depolymerisation of lignins, either via the oxidation of the secondary or primary alcohols.…”

Palladium‐catalyzed decarboxylative coupling of α,β‐unsaturated carboxylic acids with aryl tosylates

“…Pd(acac) 2 /CuI-catalyzed decarboxylative coupling of 1-bromo-4-methylbenzene and cinnamic acid with the assistance of PPh 3 and phen at 160°C was achieved in a yield of 91% (Scheme 1, equation (1)). A notable elegant exception was developed by Satoh and coworkers, [43] which indicated the potential of the replacement of aryl halides with arylboronic acids. Goossen et al [40] accomplished similar PdBr 2 /CuBr-catalyzed decarboxylative reaction under ligand-free conditions at 170°C in a 79% yield (Scheme 1, equation (2)).…”

Decarboxylative and dehydrative coupling of dienoic acids and pentadienyl alcohols to form 1,3,6,8-tetraenes

“…It is rare to use a pentadienyl electrophile [35], or to have a diene or simple alkene adjacent to the carboxyl group [20,36–39]. Despite the absence of this type of reactivity, the decarboxylative coupling of a pentadienyl dienoate ( 9 ; Scheme 2) was desirable enough for our group’s synthesis of clinprost that we attempted the reaction [40–41].…”