Palladium‐Catalyzed Direct Arylation of Azulene Based on Regioselective C−H Bond Activation

Abstract

An efficient synthesis of arylazulenes involving minimal steps was developed. The combination of Pd(OAc) 2 / XPhos as ac atalysta nd pivalica cid as an additive was key for the direct arylation of CÀHb onds, and the reactionp roceeded preferentially at the 1-and 3-positions of azulene, without heteroatom-containing directing groups. Compared with the traditional cross-coupling protocol, the arylation method described here requires fewer steps and uses commerciallya vailables ynthetic blocks. The degree of conjugation and the optical properties of the resulting azulenec onjugates can be adjusted by simple protonation, whicha llows the current method to be an efficient strategy for exploiting novel azulene-based functional materials.[a] Dr.

Application of Azulene in Constructing Organic Optoelectronic Materials: New Tricks for an Old Dog

“…developed a photoarylation to prepare 1‐arylazulenes by direct C−H functionalization of azulene with aryl iodides. Murai and co‐workers reported a similar strategy to Dyker's for constructing 1‐ and/or 3‐substituted azulene derivatives by direct C−H bond arylation. Furthermore, a gold‐catalyzed direct C−H alkynylation of azulenes was recently reported by Novák and co‐workers .…”

Metal‐Catalyzed C−H Bond Activation of 5‐Membered Carbocyclic Rings: A Powerful Access to Azulene, Acenaphthylene and Fulvene Derivatives

“…Then, a few groups extended the arylation of azulenes using modified reaction conditions . The Pd‐catalyzed direct arylation of guaiazulene with a variety of aryl bromides has been reported by our group in 2013 (Scheme and Scheme ) .…”

“…In 2016, Murai, Takai et al. reinvestigated the palladium‐catalyzed direct arylation of azulenes (Scheme ) . They succeeded in obtaining better yields than Dyker (see Scheme ) for mono‐C1‐arylated azulenes using 5 mol % Pd(OAc) 2 associated to 10 mol % XPhos ligand as catalytic system and a mixture of PivOH and K 2 CO 3 as base.…”

“…Then, af ew groups extended the arylation of azulenes using modifiedr eaction conditions. [7][8][9] The Pd-catalyzed directa rylation of guaiazulene with av ariety of aryl bromides has been reportedb yo ur group in 2013 (Scheme 2a nd Scheme 3). [7] Both sp 2 and sp 3 CÀHb onds of guaiazulene have been functionalized, as the nature of the cation of the base was found to allow the controlo ft he regioselectivity of the arylation, giving rise to C2-or C3-arylated guaiazulenesa nd also to 4benzylguaiazulenes.T he coupling of guaiazulene with 4-bromobenzonitrile using 2mol %P dCl(C 3 H 5 )(dppb) as catalyst, DMA as solventa nd KOAc as base afforded am ixture of the C2-and C3-arylated guaiazulenes A and B in 15:85 ratio;b y contrast, the use of al ess polar solvents uch as ethylbenzene gave am ixture of A and B in a5 3:47 ratio (Scheme2).…”

“…In 2016, Murai, Ta kai et al reinvestigated the palladium-catalyzed direct arylation of azulenes (Scheme 4). [8] They succeeded in obtaining better yields than Dyker (see Scheme 1) for mono-C1-arylated azulenes using 5mol %P d(OAc) 2 associated to 10 mol %X Phos ligand as catalytic system and am ixture of PivOH and K 2 CO 3 as base. The higher yields obtained using this procedure are probablyd ue to the use of this mixture as base, which promotes the concerted metalation-deprotonation mechanism.…”