Microwaves in Intramolecular 1,3-Dipolar Cycloaddition
| Authors | |
|---|---|
| Year of publication | 2003 |
| Type | Article in Proceedings |
| Conference | Speaker's presentation & materials |
| MU Faculty or unit | |
| Citation | |
| Field | Organic chemistry |
| Keywords | 1;3-dipolar cycloaddition; microwave-initiated; intramolecular reaction |
| Description | In our paper we would like to inform about our results with application microwave initiated process under solvent-free conditions. The reaction was carried out as one pot process when the 1,3-dipole was generated in situ by the reaction of o-allyloxybenzaldehyde 1 (sometimes ç{-substituted with substituents R1, R2) with a secondary amine 2 containing electron-withdrawing group. Influence of the substitution at the side chain double bond as well as the substitution at the nitrogen atom and electron-withdrawing groups at amine upon the yield and stereochemistry of products were searched. Reactions were carried out at both the classical heating and under microwave initiation. As the best conditions found for the microwave initiated reactions was temperature 2000C and the reaction time 15 min. At lower temperature the conversion was not full, at higher temperature a decomposition of intermediates as well as products occurred. It has been proved rather high sensitivity of the chemical reaction on the bulkiness of substituents bound at nitrogen atom of amine. The bulky substituents like terc-butyl, 1-adamantyl did not react, the reaction with isopropyl group was retarded. This observation corresponds to sterical demands of the molecule of 1,3-dipole when enters into reaction with intramoleculary bound dipolarophile. The reactions with unsubstituted allyloxy group proceed with excellent stereoselectivity when only one stereoisomer is formed. The same stereoselectivity was observed when dipolarophiles in cis-configuration at double bond bound in side chain of aromatic ring playing dipolarophile role were used (only one steroisomer was formed). When the configuration on double bond was trans two stereoisomers were isolated in different ratio depending on the nitrogen substitution R3. Nevertheless, the generated ylide always in the reaction possessed anti conformation. We suppose the transition state and its sterical demands influence the stereochemistry of the product formed. |
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