Gioia Morganti

Hemithio-analogues of meisenheimer complexes and sulphide group activation of aromatic substitution by alkoxides

Abstract EtO− in DMSO adds to ethylthiopicrate at C-3 to generate an ephemeral -adduct which ends into 1-ethylthio-4-ethoxy-2,5-dinitrobenzene, whilst ethyl picrate gives two adducts of attack of EtS− at C-3 or C-1.

New functionalized cycloheptatrienes via tropone σ-adducts

We report that, on treatment with phenyl-lithium, followed by triethyloxonium tetrafluoroborate in diethyl ether at –78°C, (i) 2-chloro- and 2-bromo-tropone give the corresponding 1-ethoxy-2-halogeno-7-phenylcycloheptatriene; (ii) 2-fluorotropone gives 2-ethoxy-3,7-diphenylcycloheptatriene; and (iii) tropone affords 1-ethoxy-2-phenylcycloheptatriene. Conceivably, in case (i) the tropone undergoes phenyl-lithium attack at C-7, followed by O-alkylation of the enolate, while in case (iii) the intermediate enolate suffers base-catalysed rearrangement and, finally, in case (iii) nucleophilic replacement of fluorine by phenyl-lithium from the tropone precedes phenyl-lithium attack at C-7 of the resulting 2-phenyl-tropone. This gives a better synthesis, than those available so far, of 2-chloro-7-aryltropones; in addition, a 1-alkoxy-2-chloro-7-phenylcycloheptatriene undergoes selenium dioxide oxidation to 2-chloro-7-phenyltropone.

Some peculiar cases of 7-telesubstitution by anionic phosphorus nucleophiles on 2-halotropones

Abstract Both 2-chloro- and 2-fluoro[3,5-2H3]tropone were found to react with lithium diphenylphosphide in tetrahydrofuran to give 2-diphenylphosphino[4,6-2H3]tropone in what constitutes the first example of telesubstitution by an anionic nucleophile in a non-protic solvent on tropones carrying nucleofugal groups; lithium diphenylphosphide oxide showed the same behaviour.

Chiral laser photochemistry: photoresolution accompanying photoisomerization of (±)-1-acetyl(benzoyl)aminobicyclo[3.2.0]hepta-3,6-dien-2-one to optically active 7-isomers. A photochemical procedure for chirality enhancement of (–)-(1S,5S)-7-acetylaminobicyclo[3.2.0]hepta-3,6-dien-2-one

Photoisomerization of (±)-1-acetylaminobicyclo [3.2.0]hepta-3,6-dien-2-one (±)-(2b) with u.v. left circularly polarized light up to 36% conversion led to (–)-(1S,5R)-(2b)[optical purity, o.p. 0.83%; ΔIµmax.(347)–4.2 dm3 mol–1 cm–1] and (–)-(1S,5S)-7-acetylaminobicyclo[3.2.0]hepta-3,6-dien-2-one (–)-(3b)[o.p. 1.5%; ΔIµmax.(345)–3.3]. The optical purities obtained allowed us to measure circular dichroism for λ > 260 nm. An analogous procedure when applied to the benzoylamino-derivatives gave ΔIµmax.(348)–5.0 and ΔIµmax.(346)–4.9 for the 1- and 7-derivatives, respectively. Further chirality enhancement to o.p. 2.9% permitted a complete (>200 nm) c.d. spectrum to be obtained for (–)-(3b).

A neutral, isolable covalent adduct between piperidine and a troponoidal phosphonium salt: A peculiar acylphosphorane

Abstract The phosphonium salt obtained by P-methylation of 2-diphenyl-phosphinotropone with methyl iodide was found to undergo C-7 addition by piperidine, and loss of hydrogen iodide, to give an acylsphosphorane which could be isolated; the regiospecificity of piperidine addition was proven by deuterium labeling at the troponoid ring.

Notizen: Regiospecific Synthesis of 1,2-Dialkylthio-7(alkyl-or aryl)thiocycloheptatrienes and 1,2-Dialkylthio-7-alkoxycycloheptatrienes

Abstract Hydride abstraction by trityl tetrafluoborate from a mixture of cyeloheptatriene[1,2]-and cycloheptatriene[3,4]-p-dithiine gave tropenylium[1,2]-p-dithiin tetrafluoborate. The latter was found to add either methoxide or various thiolates only at the tropenylium C-3, which constitutes the first entry to regiospecifically trifunctionalized cycloheptatrienes. In contrast, cycloheptatriene[1,7]-p-dithiine or various other cycloheptatrienes substituted at C-7 with either methylthio or t-butylthio groups were found to undergo alkylthiolate abstraction by trityl tetrafluoborate. This limits the usefulness of the above synthetic methods for polyfunctionalized cycloheptatrienes.

Reactions of 2-fluorotropone with Grignard reagents

On the addition of ethylmagnesium bromide to 2-fluorotropone in tetrahydrofuran, direct substitution of fluorine occurs to give 2-ethyltropone which, under the reaction conditions, undergoes, to some extent, Grignard addition at C-7 to give an intermediate enolate. The latter either acts as an O- andC-nucleophile, competing in the replacement of fluorine from unchanged 2-fluorotropone, or undergoes C-protonation during work-up to give a mixture of cis- and trans-2,7-diethylcyclohepta-3,5-dien-1 -one. All the products have been separated by chromatography. A similar reaction scheme applies to other alkyl and aryl Grignard reagents.

Chemistry of a meisenheimer-type σ-adduct derived from a troponoid

Abstract The gem-dimethoxy σ-adduct of methoxide addition to 2-methoxy-3-nitro-4,5-benzotropone reacts with either (C 2 H 5 ) 3 OBF 4 , to change the nitronate into an oxime function, or (CH 3 ) 3 SiCl, to give 2-carbomethoxy-1-nitronaphthalene and the nitronic acid corresponding to the starting adduct.

Reaction of tropone with 2-mercaptoethanol: 1,2-difunctionalization of cycloheptatrienes with oxygen and sulphur in a fused ring

Die Umsetzung von Tropon (I) mit 2-Mercaptoethanol liefert uberraschend die isomeren Oxathiine (II) und (III), die durch Hochdruckflussigkeitschromatographie getrennt werden.

A neutral thiolate–cycloheptatrienone adduct: the first direct evidence of base addition at two different, unsubstituted cycloheptatrienone carbon atoms

2-(Dimethylthio)tropone tetrafluoroborate gives a ca. 1:1 equilibrium mixture of two neutral adducts after methanethiolate attack at C(3) and C(7), which slowly change into the adduct of methanethiolate attack on 2(methylthio)tropone.