Heterocyclic Natural Products Synthesis Using Reactive Meleimides that effect Asymmetric Cycloaddition with Unreactive Dienes

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Enantiomerically pure N-substituted alpha-(2-exo-hydroxy-10-bornylsulfinyl)maleimides have been synthesized diastereoselectively. N-3-butynyl-, N-TBDMS- and N-p-methoxybenzyl maleimides obtained undergo Diels-Alder reactions with cyclopentadiene as well as furan to give the corresponding cycloadducts with a high degree of diastereoselectivity.The Diels-Alder adduct derived from the N-butynyl maleimide and cyclopentadiene was transformed into a gamma-hydroxy lactam via regioselective reduction followed by desulfinylation. The gamma-hydroxy lactam obtained has been further transformed into (+)-indolizidine and (+)-trachelanthamidine by diastereoselective N- acyliminocyclization and retro Diels-Alder reaction (flash vacuum pyrolysis) as key steps.By the similar methodology, the Diels-Alder adduct derived from the N-TBDMS maleimide and cyclopentadiene has been converted into (+)-elaeokanines A and C.The Diels-Alder adduct with the N-p-methoxybenzyl maleimide and furan was transformed into a chiral gamma-hydroxy lactam which has been further converted into a useful, chiral synthetic precursor, 5-substituted3- pyrrolin-2-one and 2,5-cis-disubstituted pyrrolidine derivative through diastereoselective N-acylimino addition and retro Diels-Alder reaction that was effected by heating in xylene.