Benzofurans, Volume 29

I. Benzofurans 1

1. Introduction and Nomenclature 1

2. Benzofuran and Its Alkyl Derivatives 2

A. Preparation 2

a. Catalytic Dehydrocyclization 2

b. Cyclization of Allyphenols 2

c. Cyclodehydration of Aryloxy ketones 3

d. Rearrangement of O-Aryloximes 5

e. Dehydrogenation of Bz- AIkyldihydrohenzofurans 6

f. Reduction of 2-Acetonyl-o-benzoquinols 7

g. Hydrogenation of 2-Acetylhenzofuran 8

h. Reaction of Copper Acetylides with Aryl Halides 8

i. Decarboxylation of Benzofurancarboxylic Acids 9

j. Photochemical Formation of Benzofurans 9

k. Adsorptive Cyclization 11

l. Condensation of Methylene Bis (ethyl sulfone) with Salicylaldehydes 12

3. Aryl benzofurans 13

A. Preparation 13

a. Cvdodehydration of io-Arloxyacelophenones 13

b. Condensation of Benzoins with Phenols 19

c. f ,3-Dipolar Additions of Oxocarbenes 20

d. Copper-Catalyzed Decomposition of Diazoketones 21

e. Ethynation of P-Benzoquinone 21

f Oxidation of Flavylium and Pyrylium Salts 22?

g. Algar-Flynn-Oyamada Oxidation of 2'-Hydroxy- chalcones 24

h. Acid-Catalyzed Cyclization of O-Aryloximes 24

i. Photolytic Cyclizations 25

j. Miscellaneous 25

4. Halobenzofurans 28

A. Chloro Derivatives 28

B. Bromo Derivatives 28

C. Iodo Derivatives 29

D. Fluoro Derivatives 29

5. Nitrobenzofurans 33

6. Benzofuranols 34

7. Aminobenzofurans 42

8. Benzofuranq uinones 53

9. Miscellaneous Reactions and Properties 56

A. Catalytic Hydrogenation 56

B. Oxidation 59

C. Ozonolysis 60

D. Nitration 62

E. Halogenation 62

F. Benzofuranylmetallic Compounds 63

G. Friedel-Crafts Techniques 65

H. Hoesch and Gatterman Techniques 67

I. With Diazoalkanes 67

J. With Dihalocarbene 68

K. Cyclophotochemical Addition 68

L. Polymerization 69

M. Miscellaneous Reactions 69

References 70

II. Acylbenzofurans 78

1. Formylbenzofurans

2. Acylbenzofurans

3. Miscellaneous reactions

A. Reduction 89

B. Oxidation 89

C. Alkaline Degradation 90

D Rearrangement of Acylbenzofuran Oximes 97

E. Rearrangement (Migration) in Acylbenzofurans 101

F. Willgerodt-Kindler Reaction 102

G. Wittig Reaction 102

H. Miscellaneous 104

References

III. Benzofurancarboxylic acids 111

1. Benzofuran monocarboxylic Acids 111

A. 2-Benzofurancarboxylic Acids 111

B. 3-Benzofurancarboxylic Acids 114

C. Hydroxybenzofurancarboxylic Acids 117

2. Benzofuran Dicarboxylic Acids 120

3. Benzofuranylalkanoic Acids 124

A. Benzofuranylacetic Acids 124

B. Benzofuranylpropionic Acids 126

C. Benzofuranylbutyric Acids 128

D. Miscellaneous Benzofuranylalkanoic Acids 130

A. Halogenation 132

B. Chloromethylation 132

C. Nitration 132

D. Saponification 135

E. Catalytic Hydrogenation 135

F. Peroxide Formation and Ozonolysis 135

G. Acylation 138

H. Alkylation 139

I. Miscellaneous Reactions 139

References

IV. Hydrogenated Benzofurans 143

1. Dihydrobenzofurans 143

A. Alkyl- (or Aryl-) Substituted 2,3- Dihydrobenzofurans 143

B. Halogen-Substituted 2,3-Dihydrobenzofurans 155

C. Nitro-Substituted 2,3-Dihydrobenzofurans 157

D. Amino-Substituted 2,3-Dihydrobenzofurans 161

E. 2,3-Dihydrobenzofuranols 165

F. Geometrical Isomers of 2,3- Dihydrobenzofurans 181

G. Miscellaneous Reactions of 2,3- Dihydrobenzofurans 186

a. Heterocyclic Ring Opening 186

b. Halogenation and Chloromethylation 188

c. Acylation 188

d. Dehydrogenation 190

e. Mercuration 190

f. Miscellaneous 190

2. Bz-Dihydrobenzofurans 192

3. Tetrahydrobenzofurans 192

4. Hexahydrobenzofurans 198

5. Octahydrobenzofurans 199

References 202

V. Benzofuranones 210

1. 3(2H)-Benzofuranones 210

A. Preparation 210

B. Reactions 220

2. Substituted 3(2H)-Benzofuranones 227

A. 2-Hydroxy-2-benz.yl-3(2H)-Benzofuranones 227

B. 2-Benzyl-3(2H)-benzofuranones 242

C. 2-Acyi-3(2H)-benzofuranones 243

D. Hydroxy Bz-Substituted 3(2H)-Benzofuranones 245

E. Reactions of Hydroxy-Substituted 3(2H,-Benzofuranones 246

3. 2(3H)-Benzofuranones 251

A. Preparation 251

B. Miscellaneous Reactions 267

4. 2,3-Dihydrobenzofurandiones 279

A. Preparation 279

B. Miscellaneous Reactions 284

References 289

VI. Naturally Occurring Benzofurans 297

1. Benzofurans 297

A. 5-Methoxybenzofuran 297

B. Furoventalene 297

C. Euparin 299

D. 5,6-Dimethoxy-2-isopropenylbenzofuran 300

E. Ageratone and Dihydroageratone 300

F. Pongamol 301

G. Tremetone Dehydrotremetone and Hydroxytremetone 302

H. 2-(6-Hydroxy-2-methoxy-3,4-methylenedioxyphenyl) benzofuran 311

I. Pterofuran 312

J. Eupomatene 313

K. Egonol 315

L. 2-(3' 4'-Dimethoxyphenyl)-5-(3"-hydroxypropyl)- 7-methoxybenzofuran 319

2. 2,3-Dihydrobenzofurans 320

A. Anisoxide 320

B. Remirol 321

C. Obtusafuran 323

D. Melanoxin 323

E. Hordatines A and B 324

3. 2(3H)-Benzofuranones 326

A. Xylerythrin 326

B. Calycin 328

4. 3(2H)-Benzofuranones 329

A. Maesopsin 329

B. Alphitonin 331

C. Aurones 332

a. Aureus in and Aureusidin 334

b. Cernuoside 335

c. Leptosin and Leptosidin 336

d. Sulfuretin and Sulfurein 337

e. Palasilrin 338

f. Hispidol 339

g- Maritimein and Maritmetin 340

h. Rengasin 341

i. Bracteatin and Bractein 342

D. Synthetic Aurone Analogs 343

E. Chemical Properties 343

References

VII. Naturally Occurring Spirobenzofuranones 370

1. Spiro-3 (2H)-benzofuranones 370

A. Griseofulvin 370

a. Nomenclature 370

b. Structure 371

c. Synthesis of Griseofulvin and Its Analogs 379

d. Dehydrogriseofulvin 385

e. Dechlorogriseofulvin 388

f Spirocyclic Compounds Related to Griseofulvin 390

g. Detection and Estimation 416

h. Biosynthesis of Griseofulvin 416

i. Metabolism 418

j. Biological Activities 419

k. Structure-Activity Relations 420

B. Geodin and Erdin 422

2. Spiro-2(3H,-benzofuranones A. Picrolichenic Acid 425

References 426

VIII. Less Common and Modified Naturally Occurring Benzofurans 431

1. Less Common Benzofurans 431

A. Menthofuran 431

B. Evodone 433

C. Bisabolangelone 434

D. Curzerenone Epicurzerenone and Isofuranogermacrene 435

E. Isosericenin. Sericealacetone and Deoxysericealactone Methyl Esters 437

F. ( +/- )-Loliolide [( + )-Digiprolactone)] 439

2. Modified Benzofurans 441

A. Usnic Acid 441

B. Isousnic Acid 451

3. Applications of Benzofurans 452

References 458

Author Index 463

Subject Index 491