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A step toward control of a noxious weed The parasitic plant Striga hermonthica causes extensive crop losses, particularly in Africa. Strigolactone hormones can be used to initiate germination of Striga seeds when no host crop is present, which causes the nascent Striga plants to die. Unfortunately, strigolactones are also used by crop plants to establish beneficial mutualisms. Uraguchi et al. developed a hybrid molecule that can initiate Striga germination without interfering with strigolactone-dependent events in the host (see the Perspective by Bouwmeester). The compound has the potential to diversify routes toward protecting fields from Striga infestation. Science , this issue p. 1301 ; see also p. 1248

γ-Lactam derivatives with multiple contiguous stereogenic carbon centers are ubiquitous in physiologically active compounds. The development of straightforward and reliable synthetic routes to such chiral structural motifs in a stereocontrolled manner should thus be of importance. Herein, we report a strategy to construct polycyclic γ-lactam derivatives that contain more than two contiguous stereogenic centers in an enantioselective as well as atom-economic manner. Moreover, we have achieved the first enantioselective synthesis of strigolactam derivative GR-24, a racemic variant of which is a potential seed germination stimulator and plant-growth regulator. A key of the procedure presented here is a nickel(0)/chiral phosphoramidite-catalyzed asymmetric [2+2+1] carbonylative cycloaddition between readily accessible ene-imines and carbon monoxide, which proceeded enantioselectively to furnish up to 90% ee (99% ee after recrystallization). The results of mechanistic studies, including the isolation of a chiral heteronickelacycle, support that the enantioselectivity on the two contiguous carbon atoms of the γ-lactams is determined during the oxidative cyclization on nickel(0).

The parasitic plant