Léon Ghosez

Cycloadditions of dichloroketene to olefins and dienes

Abstract Dichloroketene, as obtained in situ by dehydrohalogenation of dichloroacetyl chloride with triethylamine or zinc dehalogenation of trichloroacetyl bromide, is a reactive and unstable molecule. It reacts very readily with conjugated dienes to give exclusively derivatives of α,α dichlorocyclobutanone. No 1,4-cycloadducts were detected. Other activated olefins such as indene or dihydropyran also give good yields of cycloadducts. Electrophilic olefins such as methyl methacrylate or methyl fumarate are completely inert toward dichloroketene. Unlike less reactive ketenes, dichloroketene reacts readily even at room temperature with such unactivated olefins as cyclopentene and cyclohexene. However such bicyclic olefins as norbornene or norbornadiene are shown to be poor ketenophiles. These results point to a concerted cycloaddition involving an orthogonal approach of the ketene and olefin in accordance with Woodward and Hoffmanns suggestion. The scope and synthetic utility of these cycloadditions are discussed.

1-aza-1,3-dienes - Diels-alder Reactions With Alpha,Beta-unsaturated Hydrazones

The Alpha, Beta unsaturated hydrazone reacts regioselectivity with a wide range of dienophiles to give the corresponding [4+2] adducts. Reductive cleavage of the N N bond in the adducts gives tetrahydropyridines.

N-Trimethylsilyl-bis(trifluoromethanesulfonyl)imide: a better carbonyl activator than trimethylsilyl triflate

N-trimethylsilyl-bis(trifluoromethanesulfonyl)imide (TMSNTf2) was readily prepared from allyltrimethylsilane and bis(trifluoromethanesulfonyl)imide. It was shown to complex carbonyl groups much more effectively than trimethylsilyl triflate. As a result, TMSNTF2 was found to be superior to TMSOTf as a catalyst for the Diels-Alder reaction of methyl acrylate with various dienes

A Diels-alder Route To Pyridone and Piperidone Derivatives

Es wird zunachst gezeigt, das bei der Diels-Alder-Reaktion von 2-Aza-1,3-dienen konformative Faktoren eine wesentliche Rolle spielen.

Study of Chiral Auxiliaries for the Intramolecular [2+2] Cycloaddition of a Keteniminium Salt To An Olefinic Double-bond - a New Asymmetric-synthesis of Cyclobutanones

Abstract ω-Unsaturated amides derived from chiral pyrrolidines can be readily converted into keteniminium salts which undergo intramolecular [2+2] cycloaddition to yield chiral cyclobutanones. Amides derived from 2,5-dimethylpyrrolidine give the best yields and high facial selectivities.

Synthesis of Alkyl-halides Under Neutral Conditions

Abstract Primary and secondary alcohols are efficiently converted to the corresponding alkyl halides under neutral conditions.

The search for tolerant Lewis acid catalysts. Part 1: Chiral silicon Lewis acids derived from (-)-myrtenal

We have shown that association of a bulky silicon group with the bis(trifluoromethallesulfonyl)imide leaving group unexpectedly enhances the electrophilic character of the R3SiNTf2 silylating agent. The presence of a chiral substituent derived from (-)-myrtenal on the silicon atom led to a Lewis acid, which efficiently catalyzes the Diels-Alder reaction of alpha,beta -unsaturated esters. Although not yet preparatively useful, the enantiomeric excesses (up to 54%) were the highest ever reported for a chiral silicon Lewis acid

Addition of carboxylic acids and cyclic 1,3-diketones to 2-dimethylamino-3,3-dimethyl-1-azirine

Abstract The reaction of 2 - dimethylamino - 3,3 - dimethyl - 1 - azirine 1 with carboxylic acids 2a-e at room temperature in inert solvents generates rearranged 1:1 adducts in 65–92% yields. These adducts are N-acyl derivatives of 2-amino, -N,N dimethyl-isobutyramide 3a-e resulting from 1,2 addition of the acid followed by 1,2 ring cleavage and transfer of an acyl group. Cyclic enolizable 1,3 diketones 4a-c react similarly with 1 to yield the corresponding rearranged 1:1 adducts 5a-c, whereas acyclic diketones or ethyl acetoacetate are inert under comparable experimental conditions.

Asymmetric Amination of Carboxylic-acids Via a Diels-alder Strategy

2-azadienes 1 which are readily prepared from acyl chlorides react with high facial selectivity with the chiral carbamoyl nitroso dicnophile 2. Reduction and hydrolysis of the adducts yield enantiomerically pure amino acids.

A practical route towards α,β-unsaturated δ-lactones based on a [3+3] strategy. Synthesis of (−)-argentilactone

Abstract The lithio derivative of methyl 3-phenylsulphonylorthopropionate 1 reacts with epoxides to give, after acidic work-up and treatment with p-toluenesulphonic acid, β-phenylsulphonyl δ-lactones 2 . These are directly converted into the corresponding α,β-unsaturated δ-lactones 3 upon treatment with triethylamine or DBU. An application of this new method to the synthesis of (−)-argentilactone 4 is described.