Within the last decades, donor-acceptor cyclopropanes have gained increasing popularity as 1,3-dipole synthons. Most of the attention has been centered on Lewis-acid activation of the donor-acceptor cyclopropanes and only recently examples of stereoselective organocatalyzed systems have emerged.<br/>Disclosed is the development of a novel organocatalytic activation mode for donor-acceptor cyclopropanes resulting in the first organocatalyzed stereoselective [3+2] cycloaddition reaction of donor-acceptor cyclopropanes. The stereoselective 1,3-dipolar reactivity of the donor-acceptor cyclopropanes is promoted by an optically active bifunctional Brønsted base catalyst.<br/>It is demonstrated, that the activation of racemic di-cyano cyclopropyl-ketones in the presence of mono- and polysubstituted nitroolefins leads to highly substituted cyclopentanes with the formation of three consecutive stereocenters in up to 98% yield, 91% ee and with consistent &gt;20:1 dr. Variations of both the donor-acceptor cyclopropane and the nitroolefin are tolerated and a number of representative examples are given.<br/>The enantiomeric excess of the cycloaddition adducts can be enriched by recrystallizations and optically pure products can be obtained. To broaden the synthetic value of the developed methodology, it is demonstrated that chemoselective transformations on the cycloaddition adduct scaffold are possible.

Directing the activation of donor-acceptor cyclopropanes towards stereoselective 1,3-dipolar cycloaddition reactions by Brønsted base catalysis

256th National Meeting (2018)

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