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Alkoksyalleny : metody otrzymywania i zastosowanie w syntezie organicznej

100%

Łysek R. , Chmielewski M.

Wiadomości Chemiczne

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2001

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tom [Z] 55, 7-8

657-691

EN

The present short review describes methods of preparation and synthetic applications of alkoxyallenes. The title compounds can be obtain by variety of methods based on elimination, substitution, addition, isomerization and alkylation reactions. Methods based on elimination reactions and on substitution of halogen, or alkoxy substituent in allenes, or propargyl derivatives are not of great importance. The most important method of preparation of alkoxyallenes is based on isomerisation of propargyl ethers. The rearrangement triple bond/allene offers possibility of introduction of alkyl or silyl substiuents by consecutive deprotonation-alkylation and/or silylation steps. Alkoxyallenes undergo readily deprotonation a to the alkoxy group by treatment with n-butyl lithium. The resulting lithium salt reacts with electrophiles such as carbonyl compounds and alkyl halides to afford substituted alkoxyallenes. Subsequent hydrolysis of alkoxyallene fragment provides a,b-unsaturated carbonyl compounds. 1-Alkoxy-1-hydroxyalkylallenes in the presence of strong bases gave alkoxydihydrofurans or tetrahydrofuranones. Alkoxyallenes subjected to [4+2]-, [2+2]-, and (1,3)-dipolar cycloaddition afford variety of heterocyclic compounds. Five- and six-membered heterocycles having exo-double bond may undergo rearrangements to form more stable compounds. Attractive chemical properties prompted many laboratories to use alkoxyallenes for the synthesis of natural products. Syntheses of (+)-goniodiol 58, methylenomycin B 71, erigerol 89, (+)-allopumilitoxin 267 A 91, lacramin A 158, cytochalastin B 159 and (š)-xanthocidin 162 are the most representative. Alkoxyallenes undergo radical, cationic and coordination polymerization providing polymers having exo-methylene groups. In certain cases, alkoxyallenes may undergo spontaneous polymerization or polyaddition.

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Stereokontrolowana synteza tlenowych analogów penicylin i cefalosporyn

80%

Łysek R. , Furman B. , Borsuk K. , Chmielewski M.

Wiadomości Chemiczne

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2003

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tom [Z] 57, 5-6

391--433

EN

Synthesis of oxacephalotin and oxacephamandol which are more active then natural, containing sulfur congeners, and isolation of clavulanic acid, a patent inhibitor of (3-lactamase enzymes, directed attention of academic and industrial laboratories to the synthesis of oxygen analogs of penicillins and cephalosporins. The present review directs attention to the stereocontrol of a desired configuration in the formation of the bridgehead carbon atom. Five possible methods leading to basic skeletons of the title compounds are discussed (Scheme 1). Three of them involve nucleophilic substitution at C-4 of the azetidin-2-ones performed as inter or intramolccular process, and two of them involve cycloaddition reactions between ketenes and iminoethers, or between vinyl ethers and isocyanates. Owing to the general application stereospecificity, and high asymmetric induction, the last method seems to be most advantageous. The weak point of the nucleophilic substitution methodology is that a nuclcophilc enters 3-substituted azetidin-2-one ring preferentially anti to the existing substituent or if there is no substitutent at C-3, stereoselectivity in generation of a new stereogcnic center at C-4 is low. All methods arc illustrated by examples taken from the literature.

3

[2+2]Cycloaddition of Chlorosulfonyl Isocyanate to Chiral Vinyl Ethers

80%

Furman B. , Kałuża Z. , Łysek R. , Chmielewski M.

Polish Journal of Chemistry

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1999

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tom vol. 73 nr 1

43-54

EN

The asymmetric [2+2]cycloadditions of chlorosulfonyl isocyanate to vinyl ethers derived from sugars and hydroxy acids are presented. The account focuses on various aspects of the cycloaddition and on the transformations of the resulting [2+2]cycloadducts into clavams and 1-oxacephams. In order to rationalize the results of direction and magnitude of [2+2]cycloaddition, the stereochemical models of this reaction are discussed.

4

Synthesis of7-Substituted 5-Dethia-5-oxacephams via [2+2]Cycloaddition of Chlorosulfonyl Isocyanate to Sugar Vinyl Ethers

80%

Łysek R. , Furman B. , Kałuża Z. , Chmielewski M.

Polish Journal of Chemistry

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2000

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tom Vol. 74, nr 1

51-60

EN

Subsequent transformations of adducts consisting in detritylation, tosylation of a terminal hydroxy group and intramolecular alkylation of the nitrogen atom give corresponding tetracyclic 5-oxacephams.