544
I. Osaka
(Dong et al. 2013), and naphtho[1,2-b:5,6-b
]bisbispyrazine (NPz), respectively
(Villena-Blanco and Jolly 1967; Mikie et al. 2017). Note that 3 was further converted
into its alkylated derivatives (TZNT) (Dong et al. 2013). Interestingly, in the case
of NPz, various α-diketones could be applied for the cyclization to afford NPz
derivatives with different substituents at 2-, 3-, 8-, and 9-positions (Mikie and Osaka
2019; Yu et al. 2017). On the other hand, 1 was oxidized to form N-oxides of
(naphtho[1,2-c:5,6-c
]bis[1,2,5]oxadiazole) NOz (4) and the following reduction of
1 gave NOz (Kawashima et al. 2015a).
These heteroaromatics could be further functionalized by bromine or boronate
esters (Scheme 15.2). NTz, NSz, and NOz were easily brominated by Nbromosuccinimide (NBS) (Kawashima et al. 2015a) and TZNT was brominated
by bromine to give dibrominated compounds (NTz-Br2, NSz-Br2, NOz-Br2, and
TNTZ-Br2, respectively) in reasonably high yields (Scheme 15.2a, b). On the
other hand, it was reported that NPz did not undergo bromination by either NBS
or bromine. Thus, an alternative route was proposed in which NTz-Br2 was first
converted into dibromo-tetraaminonaphthalene by the reduction/ring-opening reaction with zinc, and the following cyclization with an α-diketone gave dibrominated
NPz (Scheme 15.2c) (Mikie et al. 2017). The introduction of boronate ester groups
was only reported for NTz, in which the iridium-catalyzed direct C–H borylation
reaction was employed to form 5,10-diborylated NTz (NTz-Bpin2) (Scheme 15.2d)
(Kawashima et al. 2013).
Interestingly, whereas the use of zinc as the reducing agent for NTz-Br2 provided
tetraaminonaphthalene, i.e., both thiadiazole moieties underwent a ring-opening
reaction, the use of NaBH 4 /CoCl 2 provided diamino-thiadiazolonaphthalene, i.e., a
one-sided ring-opening reaction selectively occurred. Thus, by applying this reaction, asymmetric hybrid naphthalene-based nitrogen-containing heteroaromatics,
in which two each of benzoxadiazole, benzothiadiazole, benzoselenadiazole, and
benzopyrazine were fused, were synthesized (Scheme 15.3) (Mikie and Osaka
2018). However, because debromination occurred at the same time, NTz2T, in
which both sides (5- and 10-positions) of NTz were substituted with alkylthiophenes
instead of bromine groups, was employed. The use of diacetyl and seleninyl
chloride as reagents for the ring-closing reaction provided [1,2,5]thiadiazolo[3
,4
-
5,6]naphtho[1,2-b]pyrazine
and
[1,2,5]selenadiazolo[3
,4
:5,6]naphtho[1,2c][1,2,5]thiadiazole derivatives (NTP2T and NTS2T) both in 90% yield. This
reaction was also applied to NSz2T. The reduction of NSz2T by NaBH 4 /CoCl 2
and the following ring-closing reaction using thionyl chloride and diacetyl also
gave NTS2T and the [1,2,5]selenadiazolo[3
,4
-5,6]naphtho[1,2-b]pyrazine system
(NSP2T) both in 92% yield (Scheme 15.3). Furthermore, this reaction was applicable to NOz2T, providing [1,2,5]oxadiazolo[3
,4
-5,6]naphtho[1,2-b]pyrazine
(NOP2T), [1,2,5]thiadiazolo[3
,4
:5,6]naphtho[1,2-c][1,2,5]oxadiazole (NOT2T),
and
[1,2,5]selenadiazolo[3
,4
:5,6]naphtho[1,2-c][1,2,5]oxadiazole
(NOS2T)
systems, using diacetyl, thionyl chloride, and seleninyl chloride as reagents for the
ring closure, respectively. All reactions had reasonably high yields of 70–80%.
All these naphthalene-based nitrogen-containing heteroaromatics and their derivatives are key compounds for the development of π-conjugated polymers. For
I. Osaka
(Dong et al. 2013), and naphtho[1,2-b:5,6-b
]bisbispyrazine (NPz), respectively
(Villena-Blanco and Jolly 1967; Mikie et al. 2017). Note that 3 was further converted
into its alkylated derivatives (TZNT) (Dong et al. 2013). Interestingly, in the case
of NPz, various α-diketones could be applied for the cyclization to afford NPz
derivatives with different substituents at 2-, 3-, 8-, and 9-positions (Mikie and Osaka
2019; Yu et al. 2017). On the other hand, 1 was oxidized to form N-oxides of
(naphtho[1,2-c:5,6-c
]bis[1,2,5]oxadiazole) NOz (4) and the following reduction of
1 gave NOz (Kawashima et al. 2015a).
These heteroaromatics could be further functionalized by bromine or boronate
esters (Scheme 15.2). NTz, NSz, and NOz were easily brominated by Nbromosuccinimide (NBS) (Kawashima et al. 2015a) and TZNT was brominated
by bromine to give dibrominated compounds (NTz-Br2, NSz-Br2, NOz-Br2, and
TNTZ-Br2, respectively) in reasonably high yields (Scheme 15.2a, b). On the
other hand, it was reported that NPz did not undergo bromination by either NBS
or bromine. Thus, an alternative route was proposed in which NTz-Br2 was first
converted into dibromo-tetraaminonaphthalene by the reduction/ring-opening reaction with zinc, and the following cyclization with an α-diketone gave dibrominated
NPz (Scheme 15.2c) (Mikie et al. 2017). The introduction of boronate ester groups
was only reported for NTz, in which the iridium-catalyzed direct C–H borylation
reaction was employed to form 5,10-diborylated NTz (NTz-Bpin2) (Scheme 15.2d)
(Kawashima et al. 2013).
Interestingly, whereas the use of zinc as the reducing agent for NTz-Br2 provided
tetraaminonaphthalene, i.e., both thiadiazole moieties underwent a ring-opening
reaction, the use of NaBH 4 /CoCl 2 provided diamino-thiadiazolonaphthalene, i.e., a
one-sided ring-opening reaction selectively occurred. Thus, by applying this reaction, asymmetric hybrid naphthalene-based nitrogen-containing heteroaromatics,
in which two each of benzoxadiazole, benzothiadiazole, benzoselenadiazole, and
benzopyrazine were fused, were synthesized (Scheme 15.3) (Mikie and Osaka
2018). However, because debromination occurred at the same time, NTz2T, in
which both sides (5- and 10-positions) of NTz were substituted with alkylthiophenes
instead of bromine groups, was employed. The use of diacetyl and seleninyl
chloride as reagents for the ring-closing reaction provided [1,2,5]thiadiazolo[3
,4
-
5,6]naphtho[1,2-b]pyrazine
and
[1,2,5]selenadiazolo[3
,4
:5,6]naphtho[1,2c][1,2,5]thiadiazole derivatives (NTP2T and NTS2T) both in 90% yield. This
reaction was also applied to NSz2T. The reduction of NSz2T by NaBH 4 /CoCl 2
and the following ring-closing reaction using thionyl chloride and diacetyl also
gave NTS2T and the [1,2,5]selenadiazolo[3
,4
-5,6]naphtho[1,2-b]pyrazine system
(NSP2T) both in 92% yield (Scheme 15.3). Furthermore, this reaction was applicable to NOz2T, providing [1,2,5]oxadiazolo[3
,4
-5,6]naphtho[1,2-b]pyrazine
(NOP2T), [1,2,5]thiadiazolo[3
,4
:5,6]naphtho[1,2-c][1,2,5]oxadiazole (NOT2T),
and
[1,2,5]selenadiazolo[3
,4
:5,6]naphtho[1,2-c][1,2,5]oxadiazole
(NOS2T)
systems, using diacetyl, thionyl chloride, and seleninyl chloride as reagents for the
ring closure, respectively. All reactions had reasonably high yields of 70–80%.
All these naphthalene-based nitrogen-containing heteroaromatics and their derivatives are key compounds for the development of π-conjugated polymers. For