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Anion alkoksyallenowy w syntezie związków naturalnych i ich analogów

Busiak B., Utecht G., Jasiński M.

Wiadomości Chemiczne

2016

[Z] 70, 1-2

3--23

Among diverse systems containing multiple bonds, cumulenes are recognized as the most reactive derivatives towards both nucleophilic and electrophilic agents, and for this reason, they are considered as important class of substrates for organic synthesis. Over the last three decades alkoxyallenes have been demonstrated as highly useful C3-building blocks for the construction of numerous N-, O-, and S-containing heterocycles, including enantiomerically pure compounds. Special attention has been paid to lithiated alkoxyallenes as suitable nucleophiles for the reactions with alkyl halides, strained heterocycles, carbonyl compounds and their derivatives. The presence of the allene unit in the initially formed adducts opens up several possibilities in the preparation of more complex systems. In this review, selected applications of lithiated alkoxyallenes in the synthesis of natural products and their analogues are discussed.

Alkoksyalleny : metody otrzymywania i zastosowanie w syntezie organicznej

Łysek R., Chmielewski M.

Wiadomości Chemiczne

2001

[Z] 55, 7-8

657-691

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.