Hiroyuki Miyano

Umpolung of tropone: The synthesis of novel 2-substituted tropones via 2-halocycloheptadienone enolates

Abstract 2-Halocycloheptadienone enolates, which were generated by the reaction of 2-halotropones with hydride, Grignard, and organolithium reagents, reacted with cationic electrophiles including tropylium ion to give 2-substituted tropone derivatives.

On the reactivity of tricarbonyl(1–4-η-cyclohepta-1,3,5-triene)iron derivatives: C–C bond formation of tricarbonyl(cycloheptatrienide)irons with 2-chlorotropone

Tricarbonyl(1–4-η-cyclohepta-1,3,5-triene)iron derivatives [(RC7H7)Fe(CO)3](R = H, OMe, CN, and Ph)(4a–d) have been prepared and a study made of the nucleophilic attack of 2-chlorotropone by their corresponding anions. The tricarbonyl(cycloheptatrienide) iron and tricarbonyl(methoxycycloheptatrienide)iron undergo the reaction to give tricarbonyl[1–4-η-7-(2-oxocyclohepta-1,3,5-trienyl)cyclohepta-1,3,5-triene]iron (7a) and tricarbonyl[1–4-η-6-methoxy-7-(2-oxocyclohepta-1,3,5-trienyl)cyclohepta-1,3,5-triene] iron (7b), respectively. In contrast, tricarbonyl (cyanocycloheptatrienide)iron reacted with 2-chlorotropone to afford tricarbonyl[1–4-η-6-cyano-7-(2-oxocyclohepta-1,3,5-trienyl)cyclohepta-1,3,5-triene]iron (7c) and tricarbonyl[1–4-η-5-cyano-7-(2-oxocyclohepta-1,3,5-trienyl)cyclohepta-1,3,5-triene] iron (9c) in a ratio of (7c)/(9c)=1:5.6. Similarly, tricarbonyl(phenylcycloheptatrienide)iron with 2-chlorotropone also affords two products, tricarbonyl[1–4-η-6-phenyl-7-(2-oxocyclohepta-1,3,5-trienyl)cyclohepta-1,3,5-triene]iron (7d) and tricarbonyl[1–4-η-2-phenyl-7-(2-oxocyclohepta-1,3,5-trienyl)cyclohepta-1,3,5-triene]iron (10d), in a ratio of (7d)/(10d)= 3 : 1. The selective formation of (7b) and the product ratios of (7c) : (9c) and (7d) : (10d) are discussed on the basis of the electronic and steric factors of the substituent in the formally unco-ordinated allyl anion on the cycloheptatrienide ring. The stereochemistry of the tropone nucleus at C-7 is deduced to be exo to the [Fe(CO)3] entity on the basis of 1H n.m.r. spectral results. The products (7a, b, d) are easily decomplexed by trimethylamine oxide to give 7-(2-oxocyclohepta-1,3,5-trienyl)- and 1-substituted 7-(2-oxocyclohepta-1,3,5-trienyl)cyclohepta-1,3,5-triene derivatives in good yields.

On the reaction of tricarbonyl (4―7-η-1H-1,2-diazepine)iron with activated acetylenes: preparation of 1-vinyl-1H-1,2-diazepine derivatives

Addition reactions of tricarbonyl(4–7-η-1H-1,2-diazepine)iron (2a) to the triple bond of dimethyl acetylenedicarboxylate (DMAD), methyl propiolate (MP), and dibenzoylacetylene (DBA) have been investigated. The stereochemical outcome is influenced by the solvent system and the acetylenic compounds employed. While the reaction of (2a) with DMAD in an aprotic solvent afforded the syn-adduct (3a) as the major product in a protic solvent the reaction resulted in inversion of stereoselectivity to give predominantly the anti-adduct (4a). The reaction of (2a) with MP or with DBA exhibited a similar change in stereoselectivity, although MP has preferential syn selectivity and DBA has high anti-selectivity. The addition reactions of 3-methyl- and 5-methyl-derivatives of (2a) with DMAD have also been studied in order to confirm the mechanism of these reactions. The decomplexation reactions of several adducts have also been studied, with a view to the preparation of 1-vinyl-1H-1,2-diazepine derivatives.

Umpolung of Tropone: Preparation of 2-Aroyl- and 2-Acyltropones

Abstract The reaction of 2-chlorotropone with DIBAH followed by aldolization with several aldehydes affords 2-(1-hydroxyalkyl)tropones, subsequent oxidation of which results in the formation of 2-aroyl- and 2-acyltropones.

Umpolung of tropone: the reaction of 2-halogenocycloheptadienone enolates with tropylium cations and several other cationic electrophiles. Preparation of novel 2-substituted and 2,7-disubstituted tropones

The reactions of 2-halogenotropones (3a–c) with hydride reagents giving 2-halogenocycloheptadienone enolates (4a–c) have been studied to provide a reverse polarity (umpolung) of tropone. The structures of 2-chlorocycloheptadienone enolate (4a) and 2-chloro-7-deuteriocycloheptadienone enolate (4D) were confirmed by 1H NMR spectral studies. The enolates were easily reacted with tropylium and substituted tropylium cations to give 2-(2,4,6-cycloheptatrienyl)tropone (8) and its derivatives, (13b–d) and (14b–d) in good yields. The other cationic electrophiles, such as benzo- and dibenzotropylium cations, di- and triphenylcyclopropenylium cations as well as tricarbonyl(cyclopentadienylium)iron and tricarbonyl(cyclohexadienylium)iron, were also reacted with the enolate to give the corresponding 2-substituted tropones (21–27) in good to modest yields. In a similar fashion, 2-halogeno-7-substituted cycloheptadienone enolates (28a–e) were generated through the reaction of 2-chlorotropone (3a) with Grignard and organolithium reagents as well as the reaction of 2-bromo-7-methoxytropone (3d) and 2,7-dibromotropone (3e) with hydride reagent. They reacted also with tropylium cation to give 2,7-disubstituted tropones (29a–e).

Substituent effects on the acid-catalyzed isomerization of 2-cyclohepta-2,4,6-trienyltropone derivatives to 2-benzyltropones

The acid-catalyzed isomerization of the cycloheptatriene ring of 2-cyclohepta-2,4,6-trienyltropones to give benzyltropones via the norcaradiene intermediate has been studied. In the cases of 7-substituted 2-cyclohepta-2,4,6-trienyltropones (1a–f), the first-order reaction rate is dependent on the nature of the substituent on C-7 of the tropone nucleus, and an electron-withdrawing substituent could accelerate the rearrangement. On the other hand, 2-cyclohepta-2,4,6-trienyltropones (2a–c), (3a–c), and (4b, d), each of which has a substituent on the cycloheptatriene ring, exhibited remarkable chemoselectivity of C–C bond cleavage of the norcaradiene intermediate. The first-order reaction rate is dependent on both the electronic nature and the position of the substituents.