Ryuji Yokoyama

Reaction of azulenes with 1-trifluoromethanesulfonylpyridinium trifluoromethanesulfonate (TPT) and synthesis of the parent azulene

2-Azulenyl trifluoromethanesulfonate was prepared by the reaction of 2-hydroxyazulene with trifluoromethanesulfonic anhydride in the presence of triethylamine as a base. Under the use of pyridine, 1-trifluoromethanesulfonylpyridinium trifluoromethanesulfonate further reacted with 2-azulenyl trifluoromethanesulfonate to give 1-(1-trifluoromethanesulfonyl-1,4-dihydropyridin-4-yl)azulenyl trifluoromethanesulfonate. Moreover, we found that azulenes also reacted with 1-trifluoromethanesulfonylpyridinium trifluoromethanesulfonate to give 4-(1-azulenyl)-1,4-dihydropyridine derivatives and 6-(1-azulenyl)-1-trifluoromethanesulfonyl-1-aza-hexa-1,3,5-triene depending on the reaction conditions. 2-Azulenyl trifluoromethanesulfonate was converted finally into the parent azulene in excellent yield by palladium-catalyzed reduction using formic acid as a reducing reagent.

[8 + 2] Cycloaddition of 8-oxoheptafulvene with cycloheptatrienefe(co)3: synthesis of tricarbonyl[(2,3,4,5-η)-11-acetoxy-1H-cyclohept[a]azulene]iron

Abstract 8-Oxoheptafulvene reacted with cycloheptatrieneFe(CO) 3 by [8+2] cycloaddition to give tricyclo[8.5.0.0 3,9 ]pentadeca-3,5,7,11,13-pentaene-2-oneFe(CO) 3 ( 3 ), which easily reacted with another 8-oxoheptafulvene under the reaction conditions to give four products. One of them was a [2+4] cycloadduct ( 5 ) having an uncommon norcaradiene structure. Two products were [8+2] cycloadducts ( 6 and 7 ) having a γ-lactone structure. The remaining product was an acylated compound ( 4 ). On raising the reaction temperature, the yields of the acylated compound increased. The [1:1] cycloadduct 3 reacted also with acetyl chloride in the presence of triethylamine to give an acetate ( 12 ), which was oxidized with o -chloranil to give 11-acetoxy-1 H -cyclohept[ a ]azuleneFe(CO) 3 ( 15 ).

Reaction of (η4-cycloheptatriene)Fe(CO)3 with haloketenes: structure and reactivity of the cycloadducts

Abstract Reaction of (η4-cycloheptatriene)Fe(CO)3 (1) with dichloroketene (2) generated by treatment of trichloroacetyl chloride with activated zinc, gave a [2+2] cycloadduct 3 along with a small amount of σ,π-allyl complex 4 and e-lactone-type 1:2 adduct 5. However, 1 reacted with 2 generated by treatment of dichloroacetylchloride with triethylamine to give a 1:2 ester adduct 13 as a main product. Complex 1 also reacted with chloroketene, which was generated by treatment of dichloroacetyl chloride with activated zinc, to give a [2+2] cycloadduct 23 in a better yield in comparison with the case of 2. The cycloadduct 3 was converted to several interesting compounds.

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

The reaction of cycloheptatriene with dichloroketene, generated by the treatment 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] hydrogen-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 decarbonylation. The reaction of 2 with diazomethane exhibits ring expansion of the four-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 lithium chloride in good yield. The reaction of 8 with triethylamine exhibits dehydrochlorination to give 3-chloro-8,8a-dihydroazulen-2(1H)-one 10 in high yield. N-(Azulen-2-yl)pyrrolidine is also derived from either 9 or 10 in good yield.