1 -Benzopyrano pyrrolidines

A family of interesting polycychc systems 106 related to pyrrolidines was obtained in a one-pot double intermolecular 1,3-dipolar cycloaddition, irradiating derivatives of o-allyl-sahcylaldehydes with microwaves in toluene for 10 min in presence of the TEA salt of glycine esters [71]. A very similar approach was previously proposed by Bashiardes and co-workers to obtain a one-pot multicomponent synthesis of benzopyrano-pyrrolidines 107 and pyrrole products 108 (Scheme 37). The latter cycloadducts were obtained when o-propargylic benzaldehydes were utihzed instead of o-allyhc benzalde-hydes, followed by in situ oxidation [72]. 

Schiff bases containing a tethered alkene react with difluorocarbene to yield c/s-fused benzopyrano[3,4-i>]pyrrolidines. An intramolecular 1,3-dipolar cycloaddition is involved. Tethered alkynes give the corresponding pyrroles <01TL533>. The reaction of 2-allyloxybenzaldehyde with N-benzylglycine also gives this tricyclic system <01TL2455>. 

The 1,3-dipolar cycloaddition reaction of non-stabilized azomethine ylides, derived from A-alkyl-cf-amino acids, with 3-nitro-2-trifluoro(trichloro)methyl-2//-chromenes produced l-benzopyrano[3,4-c]pyrrolidines in good yields." AgOAc-catalysed asymmetric 3 + 2-cycloaddition reactions of azomethine ylides with e-deficient alkenes yielded enr/o-adducts with up to 99% ee. New chiral ferrocenyl P,N-ligands possessing a benzoxazole ring as the Af-donor (35) are effective asymmetric catalysts... 

The 3 + 2-cycloaddition reaction of azomethine ylides with c-deficient alkenes produced polysubstituted l- and D-unnatural prolines. Also, phosphoramidite-(7u(OTf)2 complexes catalyse the 1,3-dipolar cycloaddition reactions of azomethine ylides with nitroalkenes to yield exo-tetrasubstituted proline esters." The 1,3-dipolar cycloaddition of non-stabilized azomethine ylides, from iV-alkyl-a-amino acids and aldehydes, with 3-substituted coumarins provides l-benzopyrano[3,4-c]pyrrolidines in good yields and high regio- and stereo-selectivity." The organocatalytic 1,3-dipolar cycloaddition of azomethine ylides, derived from azlactones, with methyleneindolinones produced spirooxindoles with high yields (up to 95%) and high diastereo- (93 7 dr) and enantioselectivity (98% ee). ... 

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