Natural product synthesis asymmetric properties

The hetero-Diels-Alder cyclization reaction of tra s-l-methoxy-3-trimethylsilyloxy-1,3-butadiene (Si) (= Danishefsky s diene) with benzaldehyde (S ) (Scheme 12.23) [217-221] is a promising reaction for evaluating the catalytic properties of Lewis acidic lanthanide centers, and has enormous potential for asymmetric synthesis of natural products (e.g., monosaccharides) [222-225]. 

The utility and efficiency of this methodology is demonstrated by the first catalytic asymmetric synthesis of (—)-phaseolinic acid , a natural product displaying useful antifungal, antitumor and antibacterial properties, as illustrated in equation 110. 

With the enantioselective intramolecular benzoin reaction established as a synthetic tool, and in combination with our efforts in the synthesis of bioactive natural products bearing a quaternary a-hydroxy ketone unit (Davis and Weismiller 1990 Heller and Tamm 1981), such as the 4-chromanone derivative (S)-eucomol (Bohler and Tamm 1967 Crouch et al. 1999), a catalytic asymmetric synthesis of various 3-hydroxy-4-chromanones brought about by the chiral triazolium salts 127, 123b and 102 as pre-catalysts was investigated (Enders et al. 2006d). The sterically different pre-catalysts were chosen in order to adjust the catalyst system to the steric and electronic properties of the substrates 128. A screening of the reaction conditions indicated 10 mol% of the... 

Enantiomerically pure non-proteinogenic amino acids have attracted recent attention due to their antibiotic [1], antifungal [2], cytotoxic [3], and other important pharmacological properties [4]. Frequently, they also occur incorporated in natural products, such as peptides, depsipeptides, and other macrocyclic compounds. Other important applications are to serve as building blocks in asymmetric synthesis. A specifically prominent class of them are cyclic 3- and y-amino acids, the subject to which the present chapter is dedicated. 

The asymmetric synthesis of the cyclopentane 66, a synthetic intermediate of the alkaloid (—)-incarvillateine 64 (a natural product with potent analgesic properties isolated firom the aerial parts of Incarvillea sinensis Lam.), via a Rh-catalyzed olefin C—H bond activation, is a follow-up of the methodology employed for the total synthesis of (-F)-litho-spermic acid disclosed by Bergman and EUman. The chiral imine 67, prepared in few steps, was submitted to [RhCl (coe)2l2 (coe = cyclooctene) as catalyst under various reaction conditions. The complete conversion of 67 occurred in the presence of a 4-(dimethylamino)phenyl... 

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