A route to pyrrolizidines, indolizidines and quinolizidines via intramolecular oxime olefin cycloadditions

Expeditious synthesis of highly substituted 3(2H)-furanone and quinoline by microwave assisted reaction between aldonitrones and dibenzoylacetylene

Microwave assisted reaction between various aldonitrones and dibenzoylacetylene gave 2-hydroxy-2,5-diphenyl-4-(phenylamino)furan-3(2H)-one (5) and (3-hydroxy-2-phenylquinolin-4-yl)(phenyl)methanone (8) arising through two distinct reaction pathways in good yields. Compared to reactions carried out under thermal...

The Domino Way to Heterocycles

Sequential transformations enable the facile synthesis of complex target molecules from simple building blocks in a single preparative step. Their value is amplified if they also create multiple stereogenic centers. In the ongoing search for new domino processes, emphasis is usually placed on sequential reactions which occur cleanly and without forming by-products. As a prerequisite for an ideally proceeding one-pot sequential transformation, the reactivity pattern of all participating components has to be such that each building block gets involved in a reaction only when it is supposed to do so. The development of sequences that combine transformations of fundamentally different mechanisms broadens the scope of such procedures in synthetic chemistry. This mini review contains a representative sampling from the last 15 years on the kinds of reactions that have been sequenced into cascades to produce heterocyclic molecules.

A Highly Stereoselective One-Pot Tandem Consecutive 1,4-Addition-Intramolecular 1,3-Dipolar Cycloaddition Strategy for the Construction of Functionalized Five- and Six-Membered Carbocycles(,)(1)

Nitronates 3, possessing a suitably located olefinic moiety and arising from conjugate addition of Grignard reagent 2 to nitro olefins 1, are trapped as silyl nitronates 8 which undergo a facile intramolecular 1,3-dipolar cycloaddition. The resulting N-(silyloxy)isoxazolidines 9 are readily transformed into isoxazolines 6 and 7 upon treatment with acid, thus completing the entire sequence in one pot. While cycloaddition to the five-membered carbocycles, in general, proceeds smoothly at rt in a stereospecific manner, that to the six-membered ring is sluggish and less selective. The advantages of this strategy over the intramolecular nitrile oxide cycloaddition, namely greater stereoselectivity and adaptability to one-pot conditions, have been demonstrated. Extensive NMR investigations unravelled the stereochemistry unambiguously and underscored the inadequacy of coupling constants alone in determining the stereochemistry in cyclopentane systems. The explanation advanced to account for the selectivities, in terms of subtle differences among the putative transition state geometries, is in qualitative agreement with widely accepted assumptions pertaining to 1,3-dipolar cycloadditions.