Letter
Nickel-Catalyzed Ring-Opening C−O Functionalization of peri-
ACCESS
*
ABSTRACT: Herein, we disclose the Ni-catalyzed ring-opening C−O functionaliza-
tion of peri-xanthenoxanthenes using Grignard reagents that forms 8-monofunction-
alized binaphthols. 1,2-Bis(dicyclohexylphosphino)ethane was the best ligand for
alkylations and ICy for arylation. After mechanistic investigations, we assumed that the
reaction proceeds via C−O reduction and subsequent C−O functionalization. To
verify the mechanism, the intermediate after reduction was isolated. Moreover, the
asymmetric addition, using 8-octylbinaphthol after optical resolution, was studied.
inaphthyl derivatives are widely applied as chiral ligands
and catalysts in many asymmetric transformations.
To prove this hypothesis, we applied the Ni-catalyzed C−O
1
B
functionalization, which experienced considerable attention in
8
,9
this past decade. There have been a few reports on C−O bond
Preferred synthetic strategies for these reagents are modifica-
tions of binaphthol (1,1′-bi-2-naphthol) using electrophilic
10
activation of diaryl ethers. Martin reported the C−O silylation
10a
2
of dibenzofuran with silylborane, and Yorimitsu and Osuka
substitutions at 6,6′-positions and directed metalations at 3,3′-
1
0b
3
disclosed the C−O arylation of dibenzofuran with ArMgBr.
positions. Although homocoupling reactions of 2-naphthol
Tobisu and Chatani developed the C−O bond alkylation of
derivatives are also available for the synthesis of binaphthol with
10c
4
diaryl ethers and dibenzofuran with Grignard reagents.
substituents in other positions, the synthesis of 8,8′-function-
We started our investigation to achieve the Ni-catalyzed ring-
opening reaction of PXX 1a employing Tobisu’s reaction
conditions (Table 1). Surprisingly, the reaction of 1a with
alized binaphthols has not been fully developed because of the
5
steric hindrance of the 8-position of binaphthol.
In our laboratory, we applied Cu-catalyzed ring-closing
reactions of binaphthol to produce peri-xanthenoxanthene
PXX) derivatives (Scheme 1a), which are used as p-type
Ni(cod) (15 mol %), 1,2-bis(dicyclohexylphosphino)ethane
2
(
dcype) (15 mol %), and n-octylmagnesium iodide (2a, 6 equiv)
(
in toluene for 40 h gave 8-n-octylbinaphthol (3aa) in 71% yield,
accompanied by small amounts of binaphthol 4 (∼9%, Table 1,
transistors for rollable displays by Kobayashi (Sony Corpo-
6
,7
11
ration). We think the reductive ring-opening reaction of PXX
to introduce substituents could result in a novel synthetic
strategy for binaphthol derivatives (Scheme 1b).
entry 1), not 8,8′-di(n-octyl)binaphthol. No reaction occurred
with the addition of other bidentate cyclohexylphosphine
ligands, such as 1,3-bis(dicyclohexylphosphino)propane
(
dcypp), 1,1′-bis(dicyclohexylphosphino)ferrocene (dcypf),
Scheme 1. Ring-Closing and Ring-Opening Strategy to
Functionalize Binaphthols
bipyridine, monodentate, and carbene ligands (entries 2−8).
The reaction of 1a with PhMgBr 2A, adding Ni(cod) and
2
dcype, was unsuccessful, with no recovery of starting materials
(
Table 1, entry 1). After optimization of the ligands, addition of
carbene ligand ICy effectively produced 8-phenylbinaphthol
11
3
aA in 58% yield (entry 6). No reactions occurred with 2A
using other ligands listed in Table 1 (entries 2−5, 7, and 8).
temperature variations were also studied (see Tables S1−S4).
Received: March 27, 2021
©
XXXX American Chemical Society
A
Org. Lett. XXXX, XXX, XXX−XXX