Asymmetric catalytic growth

The preparation of asymmetric nanosilica differs slightly from that of their symmetric counterparts, the main difference being an involvement of templates or anisotropic catalysts [28]. The addition of these materials initiates an asymmetric growth of nanomaterials, thus producing helical nano materials. In the template nanosiUca, a further treatment of as-made silica-like nanomaterials is required to convert them into real siUca nanomaterials. However, in the catalytic growth of heUcal nanomaterials such as nanocoils, no post-synthesis treatment is required. 

Catalytic, enantioselective cyclopropanation enjoys the unique distinction of being the first example of asymmetric catalysis with a transition metal complex. The landmark 1966 report by Nozaki et al. [1] of decomposition of ethyl diazoacetate 3 with a chiral copper (II) salicylamine complex 1 (Scheme 3.1) in the presence of styrene gave birth to a field of endeavor which still today represents one of the major enterprises in chemistry. In view of the enormous growth in the field of asymmetric catalysis over the past four decades, it is somewhat ironic that significant advances in cyclopropanation have only emerged in the past ten years. 

The effectiveness of this protocol was demonstrated by tbe first catalytic asymmetric synthesis of the (+)-a-methyl-3-indolylacetic acid fragment of acremoauxin A, a potent plant growth inhibitor (eq 8). 

In view of the biological importance of the 6-lactone moiety, extensive efforts have been devoted for the development of various methods for the synthesis of saturated 8-lactones. Ammig the various methods, the more classical methods include lactonization of the 8-hydroxy acid derivatives, Baeyer-Villiger oxidation of cyclopentanones, and oxidation of lactols. Besides, more challenging and attractive methods such as oxidative lactonization, radical cyclization, and carbonylatimi have also been used efficiently for the synthesis of 8-lactones. The past two decades have witnessed remarkable growth in the development of catalytic and asymmetric methods for the synthesis of 6-lactones in optically pure form. In the next decade, new and more exciting advances in the development of efficient and catalytic enantioselective methods and their application in the synthesis of complex 8-lactone natural products can be expected. 

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