[2+2] cycloaddition reaction of cycloheptatriene with dichloroketene. A novel and efficient synthetic strategy for the synthesis of 2-hydroxyazulene

Citation
R. Yokoyama et al., [2+2] cycloaddition reaction of cycloheptatriene with dichloroketene. A novel and efficient synthetic strategy for the synthesis of 2-hydroxyazulene, J CHEM S P1, (18), 2001, pp. 2257-2261
Citations number
23
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Chemistry & Analysis","Organic Chemistry/Polymer Science
Journal title
JOURNAL OF THE CHEMICAL SOCIETY-PERKIN TRANSACTIONS 1
ISSN journal
1472-7781 → ACNP
Issue
18
Year of publication
2001
Pages
2257 - 2261
Database
ISI
SICI code
1472-7781(20010921):18<2257:[CROCW>2.0.ZU;2-J
Abstract
The reaction of cycloheptatriene with dichloroketene, generated by the trea tment of trichloroacetyl chloride with activated zinc in dry diethyl ether, affords 9.9-dichlorobicyclo[5.2.0]nona-2,4-dien-8-one 2 as a major product together with 3',3',9,9-tetrachlorospiro(bicyclo[5.2.0]nona-2,4-diene-8,2' -oxetan)-4'-one 3. Structure 3 is elucidated by the X-ray crystallographic analysis of its partially reduced product. Lactone 3 exhibits [1,5] hydroge n-migration in the seven-membered ring to give 3', 3', 9,9-tetrachlorospiro (bicyclo[5.2.0]nona-3,5 -diene-8,2'-oxetan)-4'-one 7 without any decarbonyl ation. The reaction of 2 with diazomethane exhibits ring expansion of the f our-membered ring to give 1,1-dichloro-3,3a,4,8a-tetrahydroazulen-2(1H)-one 8. 2-Hydroxyazulene 9 is successfully derived by the reaction of 8 with li thium chloride in good yield. The reaction of 8 with triethylamine exhibits dehydrochlorination to give 3-chloro-8,8a-dihydroazulen-2(1H)-one 10 in hi gh yield. N-(Azulen-2-yl)pyrrolidine is also derived from either 9 or 10 in good yield.