Total Synthesis of Bioactive Tricyclic Marine Alkaloids, Lepadiformine and Related Compounds

Ó 2003 The Chemical Society of Japan

Bull. Chem. Soc. Jpn., 76, 2075–2089 (2003) 2075

Headline Articles

Photochemical Transformations of Quintet m-Phenylenedinitrenes

ꢀ;y

Sergei Victorovich Chapyshev and Hideo Tomioka

Institute of Problems of Chemical Physics, Russian Academy of Sciences,

142432 Chernogolovka, Moscow Region, Russian Federation

yChemistry Department for Materials, Faculty of Engineering, Mie University, Tsu, Mie 514-8507

Received April 21, 2003; E-mail: tomioka@chem.mie-u.ac.jp

Photochemical transformations of quintet dinitrenes have been studied for the ﬁrst time by FTIR spectroscopy dur-

ing the photolysis of 1,3-diazidobenzene and its 2-methyl- and 2,4,6-trimethyl-substituted derivatives in solid argon at 13

K. The reactions involve two competitive processes. In the ﬁrst one, the intramolecular insertion of the nitrene unit into

the 1,6-aromatic bond induces ring-opening, which leads to the formation of aminoacetylenes. The second process in-

volves the intramolecular addition of the nitrene unit to the 1,2-aromatic bond followed by ring-opening to form

4(2H-azirin-2-ylidene)-2-butenenitrile derivatives. Methyl groups in ortho-positions to the nitrene units of quintet dini-

trenes eﬃciently protect their aromatic ring from nitrene attacks, substantially increasing the photochemical stability of

such species. However, even quintet 2,4,6-trimethylphenylene-1,3-dinitrene decomposes to ring-opened products on ex-

tended irradiation. This indicates that quintet dinitrenes are much more photochemically reactive species than triplet

nitrenes. Undesirable photochemical rearrangements of the latter at early stages of the photolysis of 1,3-diazidobenzenes

are suppressed on introducing the methyl group in position 2 of these azides.

In the last decade, much attention has been focused on explo-

rations of high-spin nitrenes that are promising magnetic mate-

rials for electronics.¹Dozens of quintet dinitrenes²and several

septet trinitrenes³have now been characterized by EPR spec-

troscopy and some of them have been studied using FTIR⁴

and UV–vis spectroscopy.⁵However, nothing is known so

far about the photochemical stability and chemical transforma-

tions of quintet dinitrenes. Recent FTIR studies of singlet o-

and p-phenylenedinitrenes have shown that such species are

photochemically very labile and readily decompose to form

various ring-opened products.^6,7In comparison with singlet

o- and p-phenylenedinitrenes, quintet m-phenylenedinitrenes

have much larger energy gaps (12–15 kcal/mol)^3a,5between

their quintet-spin ground state and triplet-spin excited states

and should therefore be more photochemically stable. On the

other hand, these energy gaps for quintet dinitrenes are substan-

tially smaller than singlet–triplet energy gaps for triplet arylni-

trenes (18–22 kcal/mol).^4,5Despite these rather large singlet–

triplet energy gaps, many triplet arylnitrenes readily rearrange

into ring-expanded products on photolysis in cryogenic

matrices.⁸Such rearrangements of triplet arylnitrenes are un-

desirable reactions during the photochemical generation of

quintet dinitrenes from aromatic diazides. An eﬃcient method

to avoid the loss of high-spin products during the photochemi-

cal synthesis can be the protection of the aromatic rings from

nitrene insertion reactions by introducing appropriate substitu-

ents in ortho-positions to the nitrene units.⁴Previous studies

have found that o-methyl groups are among the best protecting

groups for such purposes.⁹Thus, for instance, triplet 2,6-di-

methylphenylnitrene is one of the most photochemically stable

triplet arylnitrenes.¹⁰In this work, we report our FTIR, EPR

and UV–vis studies of the photolysis of 1,3-diazidobenzene

and its 2-methyl- and 2,4,6-trimethyl-substituted derivatives

in cryogenic matrices, providing the ﬁrst information regarding

the photochemical behavior of quintet dinitrenes.

Results and Discussion

New diazides 2b, c were synthesized from commercially

available diamines 1b, c in a manner similar to that used for

the preparation of diazide 2a¹¹(Scheme 1).

EPR studies of the photolysis of diazides 2a–c with light at

ꢀ > 300 nm were carried out in degassed 2-methyltetrahydro-

furan (2MTHF) solutions frozen at 77 K. Figure 1 shows the X-

band EPR spectra obtained from each sample at microwave fre-

quencies of 9.243, 9.212 and 9.231 GHz. All signals remained

unchanged at 77 K for at least 2 h, but disappeared at once upon

thawing of the matrix.

An EPR spectrum obtained from the photolysis of 2a for 4

min (Fig. 1a) showed a set of signals at 79, 140, 300 (major),

380, 474, 605, 683, 840 and 982 mT and was almost identical

to that earlier reported by Murata and Iwamura.¹²The strong

peak at 683 mT is attributable to the x,y-transition of triplet azi-

donitrene 3a (jD=hcj ¼ 1:010 cm^ꢁ1and jE=hcj ¼ 0:000 cm^ꢁ1),

while all other signals can be assigned to quintet dinitrene 4a,

Published on the web November 15, 2003; DOI 10.1246/bcsj.76.2075

2076 Bull. Chem. Soc. Jpn., 76, No. 11 (2003)

HEADLINE ARTICLES

Scheme 1.

Fig. 1. EPR spectra after irradiation (ꢀ > 300 nm, 2MTHF,

77 K) of diazide 2a (ꢂ₀¼ 9:243 GHz) (a), diazide 2b

(ꢂ₀¼ 9:212 GHz) (b), and diazide 2c (ꢂ₀¼ 9:231 GHz)

(c).

Fig. 2. Diﬀerence spectrum before and after irradiation

(ꢀ > 300 nm, 1 min) of diazide 2a in Ar at 13 K.

a peak of triplet 3b at 674 mT (jD=hcj ¼ 0:978 cm^ꢁ1and

jE=hcj ¼ 0:000 cm^ꢁ1) and a set of signals for quintet 4b at

89, 165, 237, 293 (major), 399, 505, 593, 813 and 965 mT

(jD=hcj ¼ 0:202 cm^ꢁ1and jE=hcj ¼ 0:039 cm^ꢁ1). An EPR

spectrum obtained from the photolysis of 2c for 10 min

except for a weak signal at 330 mT attributable to a radical im-

purity from 2MTHF.¹²A new and important observation of this

work is the detection of a weak EPR signal of quintet 4a at 982

mT. All previous calculations^12,13of the zero-ﬁeld splitting

(zfs) D- and E-parameters of quintet 4a were based on the as-

sumption that the weak signal at 840 mT is the highest Z-tran-

sition of this quintet, and that its Y-transition overlaps with the

x,y-transition of triplet 3a at 683 mT. This allowed Murata and

Iwamura¹²to estimate the zfs D- and E-parameters of quintet

4a as jD=hcj ¼ 0:162 cm^ꢁ1and jE=hcj ¼ 0:025 cm^ꢁ1, while

similar estimations of Wasserman et al.¹³were jD=hcj ¼

(Fig. 1c) showed

a peak of triplet 3c at 658 mT

(jD=hcj ¼ 0:918 cm^ꢁ1and jE=hcj ¼ 0:000 cm^ꢁ1) and a set of

signals for quintet 4c at 72, 166, 265, 289 (major), 379, 476,

578, 634, 793 and 920 mT (jD=hcj ¼ 0:184 cm^ꢁ1and jE=hcj ¼

0:040 cm^ꢁ1). Owing to much higher intensities of all EPR sig-

nals of quintet 4c, its highest Z- and Y-transitions at 920 and

793 mT are well observable already in the main spectrum.

An increase in intensities of EPR lines of quintet dinitrenes

on going from 4a to 4c suggests that progressive methylation

of the benzene ring at ortho-positions to the nitrene centers con-

siderably increases the yields of quintet products.

0:156 cm^ꢁ1and jE=hcj ¼ 0:029 cm^ꢁ1

.

According to our

EPR studies,¹⁴quintet 4a displays its highest Z- and Y-transi-

tions at 982 and 840 mT and therefore has the zfs D- and E-pa-

rameters of jD=hcj ¼ 0:207 cm^ꢁ1and jE=hcj ¼ 0:043 cm^ꢁ1

.

These values are in good agreement with the zfs D- and E-pa-

rameters of quintet 4a (jD=hcj ¼ 0:206 cm^ꢁ1and jE=hcj ¼

0:041 cm^ꢁ1) determined by Takui et al.¹⁵with the aid of the ei-

genﬁeld simulation method.

In order to investigate in details the photochemical behavior

of quintet 4a–c, FTIR and UV–vis studies of the photolysis of

diazides 2a–c in Ar matrices at 13 K were carried out.

The presence of three IR bands at ꢁ ¼ 1611, 1605 and 1592

cm^ꢁ1as well as that of ﬁve bands in the region from 1321 to

1255 cm^ꢁ1in the IR spectrum (Table 1) of starting 2a indicated

that this diazide was present in the matrix as a mixture of three

isomers: E,Z-2a, E,E-2a and Z,Z-2a. Brief (0.25–1.5 min) ir-

The photolysis of diazides 2b, c led to the appearance of EPR

spectra of triplet 3b, c and quintet 4b, c that much resembled

the EPR spectra of triplet 3a and quintet 4a. An EPR spectrum

obtained from the photolysis of 2b for 20 min (Fig. 1b) showed

S. V. Chapyshev et al.

Bull. Chem. Soc. Jpn., 76, No. 11 (2003) 2077

ꢀ

Table 1. IR Spectrum of 2a in Ar at 13 K and B3LYP/6-31G Calculated IR Spectra of E,Z-2a, E,E-2a and

Z,Z-2a

2a/Obs

ꢁ/cm^ꢁ1

E,Z-2a/Calcd

E,E-2a/Calcd

Z,Z-2a/Calcd

I^aÞ

ꢁ/cm^ꢁ1

I^aÞ

ꢁ/cm^ꢁ1

I^aÞ

ꢁ/cm^ꢁ1

I^aÞ

—

2117

1611

1605

1592

1488

1446

—

3104

3091

3086

3073

—

0.00

—

3091

3079

3070

3047

2988

2941

2182

2176

1577

1576

1467

1460

1455

1437

1386

1331

1319

1300

1217

1184

1156

1139

1078

1032

1018

923

867

842

790

766

753

691

685

576

570

521

519

515

0.01

0.00

0.01

0.02

1.00^bÞ

0.01

0.09

0.03

0.00

0.01

0.05

0.00

0.13

0.12

0.00

0.01

0.00

0.04

0.00

0.03

0.00

0.03

0.00

0.01

0.00

3106

3101

3079

3072

—

0.00

0.01

0.00

—

2181

2175

1590

1573

1475

1432

—

0.27

1.00^bÞ

0.16

0.05

0.11

0.01

—

2184

2170

1583

1581

1479

1426

—

1.00^bÞ

0.30

0.10

0.11

0.02

—

1.00

0.09

0.10

0.21

0.03

—

1321

1295

1288

1266

1255

1170

1159

1153

1108

—

0.10

0.09

0.19

0.16

0.13

0.01

—

1335

1316

1309

1271

—

0.05

0.04

0.20

0.01

—

1333

1325

1297

1279

—

0.22

0.00

0.10

0.00

—

1157

1146

1092

1077

975

938

903

856

850

764

761

668

665

644

578

521

519

—

0.00

0.01

0.00

0.03

0.00

0.03

0.00

0.03

0.00

0.01

0.00

—

1149

1145

1098

1068

976

943

923

866

832

770

748

666

665

637

577

520

518

—

0.00

0.03

0.00

0.03

0.00

0.03

0.04

0.01

0.02

0.00

0.02

0.00

—

919

871

853

782

773

709

686

678

—

0.01

0.04

0.03

0.01

0.04

—

537

—

0.01

—

a) Relative intensity. b) Calculated intensities of IR bands of E,Z-2a, E,E-2a and Z,Z-2a at 2175, 2176

and 2184 cm^ꢁ1are 1177, 1620 and 1000 km/mol, respectively.

radiation of 2a at ꢀ > 300 nm resulted in depletion of the IR

bands of Z-3a, E-3a, 5a and 6a were in good agreement with

B3LYP/6-31G calculated IR spectra for these compounds

ꢀ

bands of starting 2a at ꢁ ¼ 2117, 1611, 1605, 1592, 1488,

1321, 1295, 1288, 1266 and 1255 cm^ꢁ1. Prominent new IR

bands appearing in the diﬀerence IR spectra (Fig. 2) at

ꢁ ¼ 1898, 1888, 1534 and 1530 cm^ꢁ1indicated the formation

(Tables 3 and 4). Our careful examinations of the diﬀerence

IR spectrum recorded after 1 min of irradiation of 2a (Fig. 2)

revealed also the presence of quintet 4a as the ﬁfth product.

Thus, the three IR bands at ꢁ ¼ 1467 (0.33), 804 (0.67) and

736 (1.00) cm^ꢁ1of this spectrum match well with the strongest

of a mixture of isomeric triplet azidonitrenes Z-3a and E-3a

8,9

(1560–1530 cm^ꢁ1

)

and isomeric didehydroazepines 5a and

6a (1900–1880 cm^ꢁ1).⁸The experimentally observable IR

UB3LYP/6-31G calculated IR bands of quintet 4a at ꢁ ¼

ꢀ

2078 Bull. Chem. Soc. Jpn., 76, No. 11 (2003)

HEADLINE ARTICLES

Table 2. IR Spectra of 2b, c in Ar at 13 K and B3LYP/6-

ꢀ

Table 3. IR Bands of Triplet 3a in Ar at 13 K and UB3LYP/

ꢀ

31G Calculated IR Spectrum of E,E-2b

6-31G Calculated IR Spectra of Triplet E-3a and Z-3a

2b/Obs

ꢁ/cm^ꢁ1

E,E-2b/Calcd

ꢁ/cm^ꢁ1I^aÞ

2c/Obs

ꢁ/cm^ꢁ1

I^aÞ

3a/Obs

ꢁ/cm^ꢁ1

E-3a/Calcd

Z-3a/Calcd

I^aÞ

ꢁ/cm^ꢁ1

I^aÞ

ꢁ/cm^ꢁ1

I^aÞ

—

2118

—

1601

1583

1562

1480

1469

1440

1383

1319

1309

1279

1226

1172

1151

1093

1072

1027

—

3111

3091

3081

3070

2181

2175

—

1595

1567

—

0

2979

2962

2934

2868

2129

2118

2109

1624

1611

1600

1593

1481

1468

1452

1442

1426

1405

1379

1330

1300

1288

1276

1221

1142

1024

1013

948

0.05

0.07

0.04

0.65

1.00

0.63

0.06

0.14

0.16

0.08

0.30

0.12

0.06

0.05

0.19

0.04

0.02

0.09

0.21

0.17

0.14

0.02

0.08

0.03

0.01

0.04

0.01

0.09

0.03

—

3111

3105

3086

3073

2178

1535

—

0.00

1.00^cÞ

0.08

—

3106

3101

3090

3077

2180

—

0.00

0.01

1.00^cÞ

—

0.01

1.00^bÞ

—

0.17

0.02

—

2109^bÞ

1534

1530

—

0.87

1.00

0.33

—

0.40

—

0.07

—

0.27

—

1.00

—

1529

1518

1428

1361

1314

1296

1250

1230

1135

1102

1062

952

939

921

855

826

754

742

641

640

0.10

0.07

0.05

0.01

0.20

0.07

0.01

0.03

0.00

0.01

0.00

0.01

0.00

0.04

0.05

0.00

0.03

0.01

0.00

0.01

0.00

0.07

0.09

0.04

0.03

0.14

0.08

0.01

0.03

0.04

0.20

0.13

0.01

0.08

—

0.06

0.04

—

1517

1424

1357

1319

1300

1249

—

0.06

0.05

0.03

0.21

0.02

0.00

—

1270

—

1237

—

814

760

—

1472

1437

1333

1324

1309

1262

—

1161

1150

1088

1082

975

931

883

863

844

760

759

690

664

0.09

0.00

0.06

0.16

0.03

—

0.00

0.01

0.00

0.01

0.00

0.02

0.04

0.00

0.01

0.00

1141

1097

1070

948

934

904

845

839

753

750

0.00

0.01

0.00

0.02

0.01

0.02

0.05

0.02

0.01

0.00

0.01

0.00

—

771

701

—

649

640

558

517

558

522

510

867

831

747

540

—

506

a) Relative intensity. b) Tail which overlaps with IR bands of

starting azide, 5a and 6a. c) Calculated intensities of IR bands

of E-3a and Z-3a at 2178 and 2180 cm^ꢁ1are 731 and 667 km/

mol, respectively.

644

579

521

518

536

—

0.01

—

that the ratio of these products in the spectrum from Fig. 2 cor-

responds to 1.0/0.8/0.5/0.2/0.4. These crude estimates sug-

gest that quintet 4a is the major (34% yield) photoproduct al-

ready after 1 min of irradiation of 2a, and that undesirable

ring-expanded products 5a and 6a are formed in 21% total

yield. Yields of triplet Z-3a and E-3a at this stage of the reac-

tion are 28% and 17%, respectively.

More extended (>1:5 min) irradiation of the matrix led to

complete disappearance of characteristic IR bands of 4a, Z/

E-3a and 5a/6a and to the appearance of many new IR bands

indicating the formation of a complex mixture of several new

photoproducts. Fortunately, some of the new IR bands were

very diagnostic. Thus, for instance, the two bands at ꢁ ¼

1819 (major) and 1797 (minor) cm^ꢁ1indicated the formation

of compounds having azirine rings.¹⁷Two very strong IR

a) Relative intensity. b) Calculated intensity of IR band of E,E-

2b at 2175 cm^ꢁ1is 1564 km/mol.

1447 (0.44), 797 (0.71) and 732 (1.00) cm^ꢁ1(Table 5). It is al-

so important to note that none of Z-3a, E-3a, 5a or 6a display

IR bands at the same wavenumbers as quintet 4a (Tables 3, 4

and 5, Fig. 2).¹⁶According to B3LYP/6-31G calculations,

ꢀ

the characteristic IR bands of quintet 4a at 732 cm^ꢁ1, triplet

Z-3a at 1528 cm^ꢁ1, triplet E-3a at 1535 cm^ꢁ1, 5a at 1885

cm^ꢁ1and 6a at 1897 cm^ꢁ1have the oscillator strengths of

34, 65, 61, 165 and 190 km/mol, respectively. Taking into ac-

count that precise relative intensities of the respective experi-

mental IR bands of quintet 4a at 736 cm^ꢁ1, triplet Z-3a at

1530 cm^ꢁ1, triplet E-3a at 1534 cm^ꢁ1, 5a at 1884 cm^ꢁ1and

6a at 1898 cm^ꢁ1are of 0.45, 0.69, 0.43, 0.34 and 1.00, we found

S. V. Chapyshev et al.

Bull. Chem. Soc. Jpn., 76, No. 11 (2003) 2079

Table 4. Experimentally Detected (Ar, 13 K) and B3LYP/6-

ꢀ

Table 5. IR Bands of Quintet 4a in Ar at 13 K and UB3LYP/

ꢀ

31G Calculated IR Bands of 5a and 6a

6-31G Calculated IR Spectrum of Quintet 4a

4a/Obs

4a/Calcd

ꢁ/cm^ꢁ1

I^aÞ

ꢁ/cm^ꢁ1

I^aÞ

5a/6a/Obs

ꢁ/cm^ꢁ1I^aÞ

5a/Calcd

ꢁ/cm^ꢁ1

6a/Calcd

ꢁ/cm^ꢁ1

—

1467

—

804

736

—

3110

3107

3103

3075

1468

1447

1392

1296

1292

1261

1252

1209

1116

1058

935

914

912

828

797

732

728

612

550

0.00

0.12

0.03

0.12

0.03

0.44

0.00

0.21

0.00

0.32

0.12

0.18

0.00

0.15

0.00

0.71

1.00^bÞ

0.03

0.32

0.00

I^aÞ

—

3108

3072

3068

3035

2175

—

0.01

0.02

0.03

1.00^cÞ

—

3095

3090

3065

3050

2177

1897

—

0.00

0.02

0.01

1.00^cÞ

0.22

—

0.33

2109^bÞ

1898

1884

—

1.00

0.33

—

1885

1574

1506

1387

1315

1307

1287

1173

1141

1057

1019

996

927

872

843

790

735

682

668

605

0.25

0.01

0.02

0.06

0.05

0.22

0.01

0.00

0.01

0.05

0.06

0.00

0.01

0.06

0.01

0.10

0.01

0.00

0.02

0.01

—

1566

1517

1369

1330

1300

1276

1198

1116

1088

1014

942

926

874

860

798

757

691

665

587

0.06

0.07

0.00

0.14

0.13

0.03

0.00

0.05

0.02

0.00

0.02

0.01

0.03

0.02

0.03

0.02

0.01

—

1342

1270

—

0.47

0.40

—

1117

1040

1021

—

0.13

0.10

0.13

—

0.67

1.00

—

796

760

697

664

583

567

516

—

0.13

0.27

0.30

0.47

0.40

0.27

0.33

—

514

a) Relative intensity. b) Calculated intensity of IR band of 4a at

732 cm^ꢁ1is 34 km/mol.

at ꢀ > 270 nm destroyed azirines 9a/11a to give 1,4-dicyano-

1,3-butadienes 13a and 13b (Fig. 3, Table 7).¹⁸The latter were

also the ﬁnal photoproducts in the photolysis of 1,4-diazidoben-

zenes⁶(Scheme 2).

Figure 4 shows the UV–vis spectra recorded during the pho-

tolysis of diazide 2a in solid argon at 13 K after 0, 35, 55, 240

and 540 min of irradiation at ꢀ > 300 nm; the inset of this Fig-

ure displays the diﬀerence spectrum obtained by subtraction of

UV spectrum of 2a from the UV spectrum recorded after 20

min of irradiation of 2a. The irradiation of diazide 2a led to

566

518

—

561

522

509

a) Relative intensity. b) Tail which overlaps with IR bands of

starting azide and triplet azidonitrenes 3a. c) Calculated inten-

sities of IR bands of 5a and 6a at 2175 and 2177 cm^ꢁ1are 678

and 858 km/mol, respectively.

bands at ꢁ ¼ 3335 and 3327 cm^ꢁ1along with a medium inten-

sity band at 3124 cm^ꢁ1and a weak band at 2117 cm^ꢁ1evi-

denced the formation of compounds with the triple carbon–car-

bon bonds. Two weak IR bands at 2219 and 2210 cm^ꢁ1also

indicated that the new compounds have cyano groups. Our ex-

a gradual decrease in intensity of its UV bands with ꢀ_max

¼

244 and 290 nm and to the appearance of new, very weak bands

in the region from 290 to 680 nm. The broad structured band in

a region from 370 to 440 nm with its maxima at 398, 407 and

428 nm as well as the very broad and weak band extending

from 520 to 680 nm with its maximum at 590 nm are typical

of triplet arylnitrenes^4,8g,9,19and can therefore be assigned to

triplet 3a. All these bands completely disappeared after 30

min of irradiation without formation of any new distinct elec-

tronic absorption bands that could be assigned to quintet 4a.

Further extended (540 min) irradiation led only to a growth

in intensity of the UV band in a region from 250 to 320 nm at-

tributable to 9a, 10a, 11a, 12a and 13a, b. The UV–vis study

ꢀ

tensive B3LYP/6-31G calculations of many possible mole-

cules showed that azirine 9a and acetylene 10a best match

the IR spectrum recorded from the photolysis of 2a for 3 h

(Fig. 3, Table 6).¹⁸It is interesting to note that very similar

photoproducts have previously been detected from the photol-

ysis of 1,4-diazidobenzene in solid argon.⁶Weak IR bands at

ꢁ ¼ 1797 and 3335 cm^ꢁ1suggest that 9a and 10a undergo pho-

tochemical isomerizations into more stable 11a and 12a. How-

ever, such isomerizations are rather ineﬃcient in the Ar

matrices. Extended irradiation of this matrix with stronger light

2080 Bull. Chem. Soc. Jpn., 76, No. 11 (2003)

HEADLINE ARTICLES

Table 6. IR Bands of 9a and 10a in Ar at 13 K and B3LYP/

ꢀ

6-31G Calculated IR Spectra of 9a and 10a

9a/Obs

9a/Calcd

10a/Obs

10a/Calcd

ꢁ/cm^ꢁ1I^aÞꢁ/cm^ꢁ1I^aÞꢁ/cm^ꢁ1I^aÞꢁ/cm^ꢁ1I^aÞ

—

3329 1.00

3369 1.00^bÞ

3081 0.10

3064 0.04

2973 0.52

2245 0.02

2112 0.02

3071 0.04

3052 0.06

—

2212 0.24 2226 0.23

—

1815 1.00 1797 1.00^bÞ

2220 0.08

2110 0.09

—

0.02

—

1.00^bÞ1630 0.10

1599 0.60 1589 0.42

1491 0.48 1496 0.42

1401 0.16 1407 0.03

0.01

0.09

0.03

0.00

0.01

0.05

1555 0.02

—

1404 0.03

1353 0.05

1222 0.02

1081 0.07

974 0.12

972 0.01

945 0.02

912 0.17

—

1366 0.05

1224 0.04

1108 0.05

—

958 0.00

916 0.02

878 0.10

856 0.07

840 0.15

804 0.08

705 0.28

700 0.14

591 0.00

—

964 0.24

—

0.00

0.13

0.12

0.00

0.01

0.00

—

851 0.24

810 0.14

721 0.30

691 0.16

—

752 0.12

749 0.43

603 0.39

567 0.00

553 0.06

770 0.59

626 0.63

—

— —

501 0.11

—

527 0.60

Fig. 3. Diﬀerence IR spectrum from photolysis (ꢀ > 270

nm, 3 h) of 2a in Ar at 13 K and theoretical (UB3LYP/

6-31G ) IR spectra of 9a, 11a, 10a, and 12a.

a) Relative intensity. b) Calculated intensities of IR bands of

9a and 10a at 1797 and 3369 cm^ꢁ1are 189 and 83 km/mol, re-

spectively.

ꢀ

demonstrates that triplet 3a is formed from diazide 2a only in

low yields and is photochemically very labile to decompose in-

to some other products without strong chromophoric groups in

their molecules already after 30 min of the photolysis. These

observations are consistent with the results of our FTIR study

of the photolysis of 2a. It is important to note that absolutely

the same UV–vis spectra were also recorded from the photoly-

sis of 2a in degassed frozen 2MTHF solutions at 77 K. The lat-

ter proves that the photolysis of 2a in both solid argon at 13 K

and in degassed frozen 2MTHF solutions at 77 K involves the

formation of the same reactive intermediates.

The IR spectrum of starting diazide 2b in solid argon at 13 K

showed major bands at ꢁ ¼ 2118, 1601, 1583, 1469, 1279,

1226, 1027, 771 and 701 cm^ꢁ1. These bands were in good

ꢀ

agreement with B3LYP/6-31G calculated vibrational fre-

Fig. 4. Photolysis (ꢀ > 300 nm) of diazide 2a in solid Ar at

13 K. UV spectra (a) before irradiation; (b) after 35 min of

irradiation; (c) after 55 min of irradiation; (d) after 4 h of

irradiation; (e) after 9 h of irradiation. In the inset is the

diﬀerence UV spectrum after 20 min of irradiation.

quencies of E,E-2b isomer (Scheme 3, Table 2). Contrary to

the case of 2a, no ring-expanded product 5b or 6b was formed

on irradiation of 2b with light at ꢀ > 300 nm. Prominent new

IR bands appearing in the ﬁrst minute of the photolysis were

S. V. Chapyshev et al.

Bull. Chem. Soc. Jpn., 76, No. 11 (2003) 2081

Table 7. IR Bands of 13a and 13b in Ar at 13 K and B3LYP/

ꢀ

6-31G Calculated IR Spectra of 13a and 13b

13a/Obs

ꢁ/cm^ꢁ1I^aÞ

13a/Calcd

13b/Obs

ꢁ/cm^ꢁ1I^aÞ

13b/Calcd

ꢁ/cm^ꢁ1

I^aÞ

ꢁ/cm^ꢁ1

I^aÞ

—

3089

3088

3076

3069

2247

2246

1616

1568

1412

1340

1239

1194

1084

987

0.03

0.00

0.08

0.00

0.43

0.00

0.08

0.00

0.06

0.00

0.03

0.00

0.17

0.00

1.00^bÞ

0.00

—

2230

—

991

—

0.20

—

1.00

—

3074

3067

3063

3062

2250

2248

1626

1592

1305

1295

1280

1207

1149

1018

993

0.15

0.00

0.02

0.00

0.48

0.00

0.14

0.10

0.00

0.06

0.00

0.05

0.00

1.00^bÞ

0.03

0.00

0.15

0.03

0.00

—

2230

—

0.31

—

955

937

950

—

0.30

—

965

936

869

791

—

858

797

757

—

1.00

—

756

732

607

527

—

618

594

514

a) Relative intensity. b) Calculated intensities of IR bands of 13a and

13b at 756 and 993 cm^ꢁ1are 65 and 66 km/mol, respectively.

Scheme 2.

manifested at ꢁ ¼ 2127, 1531, 1423, 1302, 1045 and 756 cm^ꢁ1

.

All these bands were in good agreement with UB3LYP/6-

ꢀ

31G calculated vibrational frequencies of triplet azidonitrene

E-3b isomer (Table 8). Almost the same diﬀerence IR spec-

trum was also obtained on irradiation of 2b with light at ꢀ ¼

245 nm for 2 min (Fig. 5). Triplet azidonitrene E-3b was again

a dominant product, and only very weak bands at 2104 and

1897 cm^ꢁ1(Table 9) indicating the formation of azide-substi-

tuted didehydroazepine 6b in 12% yield were observed. Previ-

ous FTIR studies^9ahave shown that the photolysis of o-tolyl

azide (14) in solid argon yields photochemically very stable

triplet o-tolylnitrene (15) (Scheme 3), which rearranges into di-

dehydroazepine 16 only on extended irradiation with light at

ꢀ > 475 nm. The irradiation of 16 at ꢀ ¼ 336 nm shifts the

equilibrium between 16 and 15 to the side of the latter. In this

respect, the absence of 6b during irradiation of 2b at ꢀ > 300

nm seems to be quite reasonable. Besides triplet E-3b, the sec-

ond major photoproduct from the photolysis of 2b is quintet 4b,

displaying the IR bands at ꢁ ¼ 1453 (0.08), 1386 (0.28), 1356

(0.25), 1267 (0.24), 1190 (0.20), 1053 (0.15) and 756 (1.00)

cm^ꢁ1(Fig. 5). These bands match well with UB3LYP/6-

ꢀ

31G calculated vibrational frequencies of quintet 4b at ꢁ ¼

1441 (0.47), 1383 (0.19), 1349 (0.21), 1294 (0.12), 1144

(0.16), 1036 (0.14) and 738 (1.00) cm^ꢁ1(Table 8). Relative in-

tensities of the characteristic IR bands of triplet E-3b at 1531

(0.0127 A, 69 km/mol) cm^ꢁ1and quintet 4b at 756 (0.0075

A, 43 km/mol) cm^ꢁ1suggest that these nitrenes are formed

in a ratio of 1:1 after 2 min of irradiation at ꢀ ¼ 245 nm. This

Fig. 5. (a) Diﬀerence spectrum before and after irradiation

(ꢀ > 245 nm, 2 min) of diazide 2b in Ar at 13 K. Theoret-

ical (UB3LYP/6-31G ) IR spectra of triplet E-3b (b), and

quintet 4b (c).

ꢀ

2082 Bull. Chem. Soc. Jpn., 76, No. 11 (2003)

HEADLINE ARTICLES

Table 8. IR Bands of Triplet 3b and Quintet 4b in Ar at 13 K

ꢀ

Table 9. Experimentally Detected (Ar, 13 K) and B3LYP/6-

ꢀ

and B3LYP/6-31G Calculated IR Spectra of Triplet 3b

and Quintet 4b

31G Calculated IR Bands of 5b and 6b

5b/6b/Obs

ꢁ/cm^ꢁ1I^aÞ

5b/Calcd

ꢁ/cm^ꢁ1

6b/Calcd

ꢁ/cm^ꢁ1

I^aÞ

3b/Obs

3b/Calcd

4b/Obs

4b/Calcd

ꢁ/cm^ꢁ1I^aÞꢁ/cm^ꢁ1I^aÞꢁ/cm^ꢁ1I^aÞꢁ/cm^ꢁ1I^aÞ

—

2104^bÞ

1897

—

1267

—

1.00

0.55

—

1.00

—

3113

3048

3047

3029

2978

2927

2173

1894

1572

1529

1451

1439

1386

1374

1318

1299

1209

1198

1098

1090

1046

1025

989

0.00

0.02

0.00

0.01

0.02

1.00^cÞ

0.18

0.02

0.04

0.00

0.01

0.16

0.01

0.02

0.01

0.05

0.02

0.00

0.01

—

3084

3053

3035

3018

2978

2927

2172

1900

1560

1508

1467

1448

1385

1381

1329

1299

1283

1192

1183

1055

1035

1019

963

0.03

0.01

0.02

0.04

1.00^cÞ

0.22

0.02

0.04

0.01

0.00

0.01

0.04

0.30

0.13

0.01

0.03

0.05

0.04

0.00

0.01

0.03

0.01

0.03

0.02

0.01

0.03

0.01

0.02

0.01

—

3103 0.01

3085 0.01

3072 0.00

3034 0.01

2985 0.01

2936 0.01

—

3105 0.14

3101 0.05

3074 0.09

3036 0.07

2981 0.16

2932 0.12

1473 0.00

1459 0.02

1449 0.19

2128 1.00 2179 1.00^bÞ

1532 0.00

1531 0.45 1517 0.09

—

1455 0.01

1452 0.01

1453 0.08 1441 0.47

1386 0.28 1383 0.19

1356 0.25 1349 0.21

1423 0.29 1410 0.07

—

1385 0.01

1362 0.00

—

1267 0.24 1294 0.12

—

1321 0.02

1303 0.80 1319 0.22

—

1280 0.09

1252 0.21

—

1280 0.03

1262 0.01

1192 0.00

1136 0.00

1130 0.00

1057 0.01

1190 0.20 1144 0.16

—

1117 0.00

1067 0.02

1053 0.15 1036 0.14

—

1008 0.02

929 0.00

895 0.05

827 0.00

791 0.02

738 1.00^bÞ

655 0.09

644 0.12

549 0.00

508 0.00

1045 0.29 1039 0.06

—

1021 0.00

928 0.00

893 0.00

840 0.00

784 0.00

754 0.06

735 0.02

670 0.01

595 0.01

561 0.00

518 0.01

511 0.00

924

905

—

801

752

723

680

627

930

888

861

792

766

735

630

624

756 1.00

0.03

0.02

0.01

0.06

0.01

0.00

0.01

—

766 0.27

744 0.10

—

599

594

505

549

536

524

—

a) Relative Intensity. b) Tail which overlaps with IR bands of

starting azide and triplet azidonitrene 3b. c) Calculated inten-

sities of IR bands of 5b and 6b at 2173 and 2172 cm^ꢁ1are 801

and 742 km/mol, respectively.

a) Relative intensity. b) Calculated intensities of IR bands of

3b and 4b at 2179 and 738 cm^ꢁ1are 763 and 43 km/mol, re-

spectively.

means that the yields of E-3b, 4b and 6b after 2 min of irradi-

ation at ꢀ ¼ 245 nm are 44, 44 and 12%, respectively. Recall

that 6b was not formed at all on irradiation of 2b at ꢀ > 300

nm.

Further irradiation of the matrix at ꢀ > 300 nm for 3 h led to

the disappearance of the characteristic IR bands of E-3b and 4b

and to the appearance of the characteristic IR bands of azirines

9b/11b and acetylenes 10b/12b (Fig. 6, Table 10). Our crude

estimates showed that 9b/11b and 10b/12b are formed in a ra-

tio of 1:10.

The formation of 9b/11b and 10b/12b from quintet 4b

shows that this quintet dinitrene is much more photochemically

labile than triplet E-3b. The main direction of photochemical

transformations of quintet 4b involves the intramolecular inser-

tion of the nitrene into 1,6-aromatic bond presumably to form

8b (path A). The latter is obviously very unstable and under-

goes the ring-opening to give acetylenes 10b/12b in 91% total

yield. At the same time, the intramolecular insertion of the ni-

trene unit into 1,2-aromatic bond (path B) followed by the ring-

opening of unstable 7b, yields azirines 9b/11b as minor (9%)

S. V. Chapyshev et al.

Bull. Chem. Soc. Jpn., 76, No. 11 (2003) 2083

Fig. 6. (a) IR spectrum after irradiation (ꢀ > 300 nm, 3 h)

of diazide 2b in Ar at 13 K. Theoretical (B3LYP/6-

ꢀ

31G ) IR spectra of 12b (b), 11b (c), and 9b (d).

triplet 3b. These bands were observed during the ﬁrst 2 min

of the photolysis of 2b and disappeared on more extended

(2–11 min) irradiation which caused the appearance of new

bands with maxima at 307, 326, 395, 418, 422 and 712 nm.

These new bands can tentatively be assigned to quintet 4b.

The very extended (>30 min) irradiation of the sample de-

stroyed the UV–vis spectrum of quintet 4b and resulted in the

appearance of the UV–vis spectrum identical to that recorded

after 540 min of irradiation of 2a. This ﬁnal UV–vis spectrum

can be assigned to a mixture of ring-opened products 9b, 10b,

11b and 12b. The results obtained show that the photolysis of

2b aﬀords triplet 3b and quintet 4b as intermediate photoprod-

ucts in quantities already suﬃcient for the UV–vis detection.

That the photochemical stability of triplet 3b and quintet 4b

is higher than that of triplet 3a and quintet 4a is consistent with

results of our FTIR studies of the photolysis of 2a and 2b.

The IR spectrum of starting diazide 2c in solid argon at 13 K

showed major bands at ꢁ ¼ 2129, 2118, 2109, 1611, 1600,

1593, 1481, 1468, 1426, 1330, 1300, 1288, 1276, 1024 and

747 cm^ꢁ1(Table 2). Such a large number of bands in the IR

spectrum of 2c is explained by a large number of rotational iso-

mers for this diazide. Due to the presence of bulky methyl

groups in ortho-positions to the azido groups, the latter comes

out of the plane of the aromatic ring in various directions, form-

ing a great variety of anti and syn E,E-, E,Z- and Z,Z-isomers.

Owing to these geometrical features, diazide 2c is rather stable

toward light at ꢀ > 300 nm and requires much more irradiation

time to be photolyzed. The irradiation of 2c with light at ꢀ >

300 nm for 30 min resulted in very slow depletion of the IR

bands of starting diazide and to the appearance of new promi-

nent bands of triplet 3c and quintet 4c at ꢁ ¼ 1506, 1447, 1437,

Scheme 3.

photoproducts. These photochemical reactions start to occur at

the stage of generation of quintet 4b from triplet E-3b, and 9b/

11b and 10b/12b become the major photoproducts already af-

ter 5 min of irradiation of 2b at ꢀ > 300 nm (Scheme 3).

Figure 7 shows the UV–vis spectra recorded during the pho-

tolysis of diazide 2b in solid argon at 13 K after 0, 1, 3, 5, 7 and

15 min of irradiation at ꢀ > 300 nm; two insets of this Figure

display the diﬀerence spectra obtained by subtraction of UV

spectrum of 2b from the UV spectrum recorded after 2 and

11 min of irradiation of 2b. As in the case of 2a, the irradiation

of diazide 2b led to a gradual decrease in intensity of its UV

bands with ꢀ_max¼ 242, 290 and 301 nm and to the appearance

of new bands in a region from 300 to 800 nm with their maxima

at 309, 324, 401, 408, 418, 422, 434, 590 and 712 nm. The

bands at ꢀ_max¼ 309, 324, 401, 408, 434 and 590 nm are typical

of triplet arylnitrenes^4,8g,9,19and can therefore be assigned to

2084 Bull. Chem. Soc. Jpn., 76, No. 11 (2003)

HEADLINE ARTICLES

Table 10. IR Bands of 9b and 10b in Ar at 13 K and

ꢀ

B3LYP/6-31G Calculated IR Spectra of 9b and 10b

9b/Obs

ꢁ/cm^ꢁ1

9b/Calcd

10b/Obs

ꢁ/cm^ꢁ1I^aÞ

10b/Calcd

I^aÞ

ꢁ/cm^ꢁ1

I^aÞ

ꢁ/cm^ꢁ1

I^aÞ

—

3081

3063

3047

3042

3014

2951

2222

1849

1596

1519

1425

1421

1405

1376

1363

1231

1187

1058

1010

975

0.02

0.05

0.04

0.00

0.01

0.20

0.56

0.20

1.00^bÞ

0.04

0.03

0.00

0.01

0.08

0.04

0.18

0.05

0.02

0.00

0.02

0.04

0.07

0.15

0.19

0.00

0.08

—

3086

3072

3048

2976

2273

2916

2246

2217

1591

1572

1448

1444

1405

1385

1342

1205

1165

1092

1031

1017

973

0.02

0.05

0.24

0.14

0.66

0.22

1.00^bÞ

0.12

0.02

0.10

0.32

0.08

0.24

0.07

0.02

0.17

0.14

0.08

0.02

0.08

0.58

0.24

0.10

0.00

0.08

—

2970

2932

2859

2221

2215

—

0.33

0.68

0.41

0.67

0.77

—

2215

1849

1624

1534

—

0.54

0.32

0.92

1.00

—

Fig. 8. (a) Diﬀerence spectrum before and after irradiation

(ꢀ > 300 nm, 30 min) of diazide 2c in Ar at 13 K. Theo-

—

1440

—

0.89

—

ꢀ

retical (UB3LYP/6-31G ) IR spectra of triplet 3c (b), and

quintet 4c (c).

—

1383

—

0.44

—

1195

—

0.38

—

1235

—

0.25

—

1064

—

0.13

—

960

911

—

917

901

—

881

802

—

765

731

—

1.00

0.30

—

768

717

—

720

701

745

—

0.46

—

711

600

677

596

—

588

522

512

—

a) Relative intensity. b) Calculated intensities of IR bands of 9b and

10b at 1519 and 2217 cm^ꢁ1are 266 and 59 km/mol, respectively.

Scheme 4.

1380, 1377, 1308, 1064, 928, 926, 875 and 708 cm^ꢁ1(Fig. 8,

Scheme 4). During all this time, no characteristic IR bands

of ring-expanded products at around 1900 cm^ꢁ1were

observed. The observable new bands matched well with

ꢀ

UB3LYP/6-31G calculated vibrational frequencies of triplet

3c and quintet 4c (Tables 11 and 12).²⁰Relative intensities

of IR bands of triplet 3c at 1065 (0.002 A, 32 km/mol) cm^ꢁ1

and of quintet 4c at 925 (0.007 A, 6 km/mol) cm^ꢁ1suggest that

the yields of 3c and 4c at this stage of the photolysis are 5 and

95%, respectively. It is interesting to note that the yield of trip-

let 3c never exceeded 5% even at the initial (1–3 min) stages of

the photolysis of 2c. As UB3LYP/6-31G calculations show,

the energy of triplet azidonitrene 3c is higher by about 13 kJ/

mol than the energy of quintet 4c + N₂.

Fig. 7. Photolysis (ꢀ > 300 nm) of diazide 2b in solid Ar at

13 K. UV spectra (a) before irradiation; (b) after 1 min of

irradiation; (c) after 3 min of irradiation; (d) after 5 min of

irradiation; (e) after 7 min of irradiation; (f) after 15 min of

irradiation. In inset is the diﬀerence UV spectra after (a) 2

and (b) 11 min of irradiation.

ꢀ

S. V. Chapyshev et al.

Bull. Chem. Soc. Jpn., 76, No. 11 (2003) 2085

Table 11. IR Bands of Triplet 3c in Ar at 13 K and B3LYP/

ꢀ

Table 12. IR Bands of Quintet 4c in Ar at 13 K and

ꢀ

6-31G Calculated IR Spectra of Triplet E-3c and Z-3c

UB3LYP/6-31G Calculated IR Spectrum of Quintet 4c

4c/Obs

4c/Calcd

ꢁ/cm^ꢁ1

3c/Obs

ꢁ/cm^ꢁ1

E-3c/Calcd

Z-3c/Calcd

ꢁ/cm^ꢁ1

I^aÞ

ꢁ/cm^ꢁ1

I^aÞ

ꢁ/cm^ꢁ1

I^aÞ

bÞ

—

0.40

—

3044

3037

3031

3013

2979

2976

2972

2933

2928

2925

1490

1485

1459

1457

1455

1446

1403

1390

1382

1381

1322

1310

1297

1274

1254

1206

1140

1023

1021

1015

1007

995

0.37

0.11

0.09

0.43

0.26

0.29

0.40

0.14

0.40

0.49

1.00^cÞ

0.12

0.37

0.20

0.43

0.26

0.14

0.03

0.23

0.03

0.00

0.63

0.03

0.11

0.06

0.00

0.03

0.09

0.03

0.06

0.37

0.06

0.17

0.20

0.06

0.14

0.00

0.03

0.00

—

3055

3034

3013

3011

2988

2981

2978

2934

2931

2928

2178

1550

1487

1462

1461

1457

1453

1448

1427

1405

1391

1389

1384

1345

1319

1287

1253

1221

1186

1046

1030

1028

1023

1019

1005

988

0.02

0.01

0.02

0.03

0.02

1.00^cÞ

0.01

0.04

0.01

0.03

0.02

0.01

0.10

0.01

0.00

0.18

0.01

0.02

0.00

0.05

0.01

0.00

0.01

0.00

0.02

0.00

0.01

0.00

0.02

0.00

3058

3028

3014

3011

2984

2981

2980

2931

2930

2929

2179

1547

1487

1464

1462

1459

1448

1447

1430

1405

1390

1388

1385

1346

1314

1288

1252

1220

1182

1051

1028

1027

1024

1018

1006

984

0.03

0.00

0.03

0.02

0.04

1.00^cÞ

0.04

0.06

0.03

0.02

0.00

0.02

0.00

0.08

0.00

0.02

0.19

0.01

0.00

0.02

0.00

0.04

0.01

0.00

0.01

0.02

0.01

0.00

0.02

0.00

bÞ

—

3010

—

bÞ

—

bÞ

—

2928

2925

1506^bÞ

0.40

0.49

0.94^bÞ

—

0.65^bÞ

1.00

—

0.41

—

0.35

0.30

—

bÞ

—

bÞ

—

bÞ

—

1447^bÞ

1437

—

bÞ

—

1377

—

1380^bÞ

0.30^bÞ

—

bÞ

—

1308^bÞ

1.00^bÞ

—

bÞ

—

1230

—

0.30

—

bÞ

—

1064

—

0.60

—

bÞ

—

925

875

—

708

—

978

908

866

824

705

684

604

551

—

920

856

921

858

—

0.40

—

819

743

838

719

—

695

622

691

623

532

—

a) Relative intensity. b) Overlaps with negative IR bands of start-

ing azide 2c. c) Calculated intensity of IR band of 4a at 1490

cm^ꢁ1is 35 km/mol.

590

553

590

560

—

542

521

544

521

—

501

519

More extended (9 h) irradiation of the matrix with light at

ꢀ > 300 nm led to the disappearance of IR bands of quintet

4c and to the appearance of IR bands of azirine 9c and acetylene

10c (Fig. 9, Table 13). These photochemical transformations

a) Relative intensity. b) Overlaps with IR bands of starting azide

2c. c) Calculated intensities of IR bands of E-3c and Z-3c at 2178

and 2179 cm^ꢁ1are 698 and 668 km/mol, respectively.

2086 Bull. Chem. Soc. Jpn., 76, No. 11 (2003)

HEADLINE ARTICLES

Fig. 9. (a) IR spectrum after irradiation (ꢀ > 300 nm, 9 h)

of diazide 2c in Ar at 13 K. Theoretical (B3LYP/6-

ꢀ

31G ) IR spectra of 10c (b) and 9c (c).

show that quintet 4c is photochemically a rather reactive com-

pound despite the protection of its aromatic ring by methyl

groups in ortho-positions to the nitrene units.

Fig. 10. Photolysis (ꢀ > 300 nm) of diazide 2c in a 2MTHF

glass at 77 K. (a) UV spectra after 0, 8, 15, 30 and 45 min of

irradiation. In inset is the diﬀerence spectrum after 8 min

of irradiation. (b) UV spectra after 0 and 300 min of

irradiation. In inset is the diﬀerence spectrum after 105

and 300 min of irradiation.

Contrary to the UV spectra of diazides 2a, b, the UV spec-

trum of diazide 2c shows only one absorption band with

ꢀ_max¼ 245 nm (Fig. 10a). Such UV spectra are typical of al-

kyl azides. This suggests that both azido groups of 2c lie out of

the plane of the benzene ring due to steric hindrance from or-

tho-methyl groups. As a result, diazide 2c was rather stable to-

ward light at ꢀ > 300 nm and required long irradiation time.

Figure 10a shows the UV–vis spectra recorded during the pho-

tolysis of diazide 2c in a degassed frozen 2MTHF solution at 77

K after 0, 8, 15, 30 and 45 min of irradiation at ꢀ > 300 nm; the

inset of this Figure displays the diﬀerence spectrum obtained

by subtraction of the UV spectrum of 2a from that recorded af-

ter 8 min of irradiation of 2a. Brief irradiation (5–10 min) of

diazide 2a led to a slow decrease in intensity of its UV bands

with ꢀ_max¼ 245 nm and to the appearance of new bands in

the region from 260 to 600 nm, with maxima at 284, 311,

326, 411, 425, 434 and 550 nm typical of triplet arylnitre-

nes.^4,8g,9,19All these bands can be assigned to triplet 3c. In

comparison with FTIR, the UV–vis spectroscopy is a much

more sensitive spectroscopic method and allows the detection

of triplet 3c despite its relatively low yield. More extended

(>45 min) irradiation led to the disappearance of bands of trip-

let 3c and to the appearance of new bands at 257, 298, 309, 328,

398, 420 and 600 nm attributable to quintet 4c. These spectral

changes are shown in Fig. 10b; the inset of this Figure displays

the diﬀerence spectrum obtained by subtraction of the UV

spectrum recorded after 30 min of irradiation of 2c from the

UV spectrum recorded after 105 min of irradiation of 2c. Rath-

er strong UV–vis spectrum of quintet 4c indicates rather high

photochemical stability of this species. This is in good agree-

ment with results of our FTIR study of the photolysis of 2c in

solid argon.

Experimental

Materials and General Methods. IR spectra were measured

on a JASCO A-100 recording spectrometer. ¹H NMR spectra were

determined with a JEOL JNM-EX 270 spectrometer. UV–vis

spectra were recorded with a Hitachi 200-S spectrometer. EPR

spectra were determined with

a

JEOL JES-TE200D

spectrometer. Column chromatography was carried out on Fuji

Davidson Silica gel BW-127ZH. Thin-layer chromatography

was done on Merck Kieselgel 60 PF254. Starting diamines 1a–c

were purchased from Tokyo Kasei Kogyo Co. Ltd.

1,3-Diazidobenzene (2a) was prepared following the literature

procedure.¹¹A mixture of m-phenylenediamine (1 g, 9.3 mmol)

and 50% sulfuric acid (20 mL) was stirred at 0–2 ^ꢂC. The diamine

dihydrosulfate was deazotized by adding sodium nitrite (1.3 g, 18.8

mmol) in small portions. To the stirred solution was slowly added

sodium azide (1.3 g, 20 mmol) in small portions at 0–5 ^ꢂC. After

the reaction mixture was stirred for an additional hour, the resulting

solution was extracted with CH₂Cl₂. The organic phase was wash-

ed (H₂O), dried (Na₂SO₄), ﬁltered, and evaporated under reduced

pressure. The residue was chromatographed on a short silica gel

column using n-hexane as an eluent. Removal of the solvent under

reduced pressure gave m-phenylenediazide (960 mg, 60%) as a

pale yellow oil. ¹H NMR (CDCl₃) ꢃ 6.65 (t, J ¼ 2:1 Hz, 1H),

6.81 (dd, J ¼ 8:1 and 2.1 Hz, 2H), 7.32 (t, J ¼ 8:1 Hz, 1H); IR

(KBr disk, thin ﬁlm) ꢁ 2968 (w), 2928 (w), 2854 (w), 2112 (vs),

1611 (s), 1586 (s), 1484 (s), 1320 (m), 1285 (s), 1262 (s), 1170

(w), 1159 (w), 1108 (w), 919 (w), 872 (w), 854 (w), 783 (w),

774 (w), 709 (w), 686 (w), 679 (w), 537 (w) cm^ꢁ1

.

S. V. Chapyshev et al.

Bull. Chem. Soc. Jpn., 76, No. 11 (2003) 2087

ꢀ

Table 13. IR Bands of 9c and 10c in Ar at 13 K and B3LYP/6-31G Calculated IR Spectra of 9c and 10c

9c/Obs

ꢁ/cm^ꢁ1

10c/Calcd

ꢁ/cm^ꢁ1

9c/Obs

ꢁ/cm^ꢁ1

10c/Calcd

ꢁ/cm^ꢁ1

I^aÞ

—

2212

1864

—

1552

—

1065

—

0.50

0.61

—

1.00

—

3040

3028

3023

3016

3011

2976

2963

2951

2925

2918

2220

1848

1611

1535

1470

1467

1447

1424

1414

1389

1386

1372

1361

1291

1173

1156

1057

1041

1033

1017

1008

968

0.05

0.13

0.02

0.00

0.05

0.09

0.13

0.02

0.17

0.21

0.27

0.62

0.12

1.00^cÞ

0.03

0.05

0.03

0.05

0.00

0.04

0.00

0.05

0.01

0.13

0.01

0.13

0.32

0.01

0.00

0.08

0.02

0.05

0.01

0.02

0.12

0.15

0.04

0.00

0.09

0.00

—

2963

—

2931

—

2862

2224

2212

1635

1580

1460

—

0.60

—

0.82

—

0.47

0.18

0.20

0.23

0.19

0.30

—

3041

3027

3021

2990

2275

2970

2969

2935

2922

2914

2247

2227

1630

1589

1460

1452

1450

1445

1444

1442

1386

1384

1375

1340

1232

1188

1135

1037

1031

1021

1020

1016

972

0.14

0.51

0.09

0.21

0.28

0.35

0.30

0.42

1.00^cÞ

0.12

0.37

0.51

0.16

0.33

0.14

0.21

0.16

0.19

0.16

0.21

0.09

0.23

0.42

0.49

0.05

0.02

0.07

0.26

0.30

0.00

0.16

0.42

0.09

0.05

0.07

0.05

0.02

1451

—

0.47

—

1438

1432

1383

1380

—

1371

1266

1218

—

1065

1028

—

747

—

0.65

0.43

0.42

—

0.23

0.28

0.25

—

0.23

0.27

—

1.00

—

bÞ

—

0.38

—

0.30

—

747

700

—

558

—

963

896

784

746

687

614

591

551

884

844

762

753

627

598

540

517

bÞ

—

543

a) Relative intensity. b) Overlaps with IR bands of 10c. c) Calculated intensities of IR bands of 9c and 10c at

1535 and 2227 cm^ꢁ1are 210 and 43 km/mol, respectively.

ꢂ

2,6-Diazidotoluene (2b) was prepared in a manner similar to

that used for diazide 2a. A mixture of 2,6-diaminotoluene (1.2

g, 9.8 mmol), water (5 mL) and concentrated hydrochloric acid

(2 mL) was stirred at 0–2 C. The diamine dihydrochloride was

deazotized by adding sodium nitrite (1.4 g, 20 mmol) in small

portions. To the stirred solution was slowly added sodium azide

(1.4 g, 20 mmol) in small portions at 0–5 C. After the reaction

mixture was stirred for an additional hour, the resulting solution

was extracted with CH₂Cl₂. The organic phase was washed

(H₂O), dried (Na₂SO₄), ﬁltered, and evaporated under reduced

pressure. The residue was chromatographed on a short silica gel

column using n-hexane as an eluent. Removal of the solvent under

ꢂ

2088 Bull. Chem. Soc. Jpn., 76, No. 11 (2003)

HEADLINE ARTICLES

reduced pressure gave 2,6-diazidotoluene (600 mg, 34%) as a light

yellow solid: mp 76–77 ^ꢂC. ¹H NMR (CDCl₃) ꢃ 2.07 (s, 3H), 6.91

(d, J ¼ 7:9 Hz, 2H), 7.24 (t, J ¼ 7:9 Hz, 1H); IR (KBr disk, thin

ﬁlm) ꢁ 2954 (w), 2926 (w), 2854 (w), 2118 (vs), 1602 (m), 1578

(s), 1559 (m), 1458 (s), 1311 (m), 1277 (s), 1255 (m), 1164 (w),

1145 (w), 1020 (w), 959 (w), 868 (w), 771 (vs), 698 (s), 537 (w)

References

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a) ‘‘Magnetic Properties of Organic Materials,’’ ed by P. M.

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Kodansha-Godon and Breach, Tokyo (2000).

cm^ꢁ1

.

2

a) S. Nimura and A. Yabe, ‘‘Magnetic Properties of Organic

1,3-Diazido-2,4,6-trimethylbenzene (2c) was prepared in a

manner similar to that used for diazide 2b. A mixture of 1,3-di-

amino-2,4,6-trimethylbenzene (1.5 g, 10 mmol), water (10 mL)

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ꢂ

and concentrated hydrochloric acid (4 mL) was stirred at 0–2 C.

The diamine dihydrochloride was deazotized by adding sodium

nitrite (2.08 g, 30 mmol) in small portions. To the stirred solution

was slowly added sodium azide (2 g, 30.8 mmol) in small portions

at 0–5 ^ꢂC. After the reaction mixture was stirred for an additional

hour, the resulting solution was extracted with CH₂Cl₂. The organ-

ic phase was washed (H₂O), dried (Na₂SO₄), ﬁltered, and evapo-

rated under reduced pressure. The residue was chromatographed

on a short silica gel column using n-hexane as an eluent. Removal

of the solvent under reduced pressure gave 1,3-diazido-2,4,6-tri-

methylbenzene (600 mg, 30%) as a colorless oil: ¹H NMR (CDCl₃)

ꢃ 2.32 (s, 6H), 2.35 (s, 3H), 6.84 (s, 1H); IR (KBr disk, thin ﬁlm) ꢁ

2954 (w), 2925 (m), 2848 (w), 2112 (vs), 1604 (w), 1474 (s), 1424

(m), 1405 (w), 1379 (w), 1326 (m), 1283 (s), 1221 (w), 1137 (w),

3

a) S. V. Chapyshev, R. Walton, J. A. Sanborn, and P. M.

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1021 (m), 868 (w) cm^ꢁ1

.

Computational Chemistry. Density functional theory²¹calcu-

lations were carried out using the GAUSSIAN 94 program.²²The

geometry optimizations for all molecules under consideration were

implemented at the B3LYP/6-31G(d) level of theory.

5

6

S. V. Chapyshev, Mendeleev Commun., 2002, 168.

A. Nicolaides, H. Tomioka, and S. Murata, J. Am. Chem.

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A. Nicolaides, T. Nakayama, K. Yamazaki, H. Tomioka, S.

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Matrix-Isolation Spectroscopy. Matrix experiments were

performed by means of standard techniques^23,24using an Iwatani

Cryo Mini closed-cycle helium cryostat. For IR experiments, a

CsI window was attached to the copper holder at the bottom of

the cold head. Two opposing ports of a vacuum shroud surround-

ing the cold head were ﬁt with KBr windows for spectroscopic

viewing, and the remaining ports were ﬁtted with quartz plate for

UV irradiation and a deposition plate for admitting the sample

and matrix gas. For UV experiments, a sapphire cold window

and quartz outer window were used. The temperature of the matrix

was controlled by an Iwatani TCU-1 controller (gold vs chromel

thermocouple).

Irradiations were carried out with a Wacom 500-W high-pres-

sure arc lamp or an Ushio 500-W mercury high-pressure arc

lamp. For broad-band irradiation, Toshiba cutoﬀ ﬁlters were used

(50% transmittance at the wavelength speciﬁed). In order to follow

the progress of reaction in detail, the intensity of the light was

tuned by changing the distance between the lamp and the window.

For typical EPR spectral experiments, an appropriate sample of

diazide was dissolved in 2-methyltetrahydrofuran (2MTHF) in a 4

mm o.d. quartz sample tube (diazide concentration of ca. 10^ꢁ4M),

subjected to a 5-fold freeze-pump-thaw degassing procedure and

sealed under vacuum, frozen at 77 K. The tube was transferred

to a Suprasilbvacuum-jacketed ﬁnger dewar, and photolyzed for

1–9 min with a Ushio 500-W mercury high-pressure arc lamp at

>300 nm (Pyrex-ﬁlter) at a distance of about 5 cm. After each ir-

radiation, the sample was placed into the cavity of a JEOL JES-

TE200D spectrometer. Most spectra were obtained over a 50–

9950 G (G) region at a modulation frequence of 100.0 kHz and a

microwave power setting of 20 dB. Microwave frequencies were

determined using a JASCO Advantest R5372 frequency counter.

The zfs D- and E-parameters of triplet and quintet nitrenes were

calculated by standard methods.^8d

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Bull. Chem. Soc. Jpn., 76, No. 11 (2003) 2089

16 For 5a and 6a, the data for only one isomer was shown in

Table for simplicity. Although other isomers might be formed, at

this stage of the reaction, the spectra are consisting of a mixture

of many products and hence it is practically impossible to assign

all the absorptions.

17 J. Backes, ‘‘Methoden der Organischen Chemie, Houben-

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e.g., 9 to 13, all possible isomers were calculated, but only isomers

whose theoretical IR bands match best the experimental IR bands

are recorded in Table.

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G. Johnson, M. A. Robb, J. R. Cheeseman, T. Keith, G. A.

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to come out of the plane of phenyl ring. Therefore, there are too

many conformers to calculate. Similarly, 3c has many possible

conformers but here in order to roughly estimate the ratio of 3c

to 4c upon irradiation of 2c, two isomers, E- and Z-3c where meth-

yl groups are ﬁxed are calculated and reported in Table.

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Article Doi

Total Synthesis of Bioactive Tricyclic Marine Alkaloids, Lepadiformine and Related Compounds

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