165450-03-3Relevant articles and documents
[1,3]-Transfer of chirality during the nicholas reaction in γ-benzyloxy propargylic alcohols
Diaz, David D.,Ramirez, Miguel A.,Martin, Victor S.
, p. 2593 - 2606 (2008/02/07)
A highly regio- and stereoselective intramolecular [1.5]-hydrogentransfer process is described. Treatment of γ-benzyl-protccted Co 2(CO)6-α,γ-acetylenic diols with BF 3·OEt2 provides bis-homopropargylic alcohols. The reaction occurs within seconds, tolerates a wide range of functionalities, and provides good yields. When the ether group is located at a stereochemically defined carbon atom, the rearrangement occurs with high stereoselectivity, transferring the chirality of the carbinol center to the newly created stereocenter. The cleavage of the benzyloxy group is totally regioselective when additional benzyl ethers are present. The scope and limitations of this novel process in densely substituted substrates are evaluated, and possible competitive reactions and/or stereochemical influences are also described. A mechanism based on a highly ordered chair-like transition state substantiated by a theoretical study is also included.
Preparation of alkyl-substituted indoles in the benzene portion. Part 15. Asymmetric synthesis of (+)-duocarmycin SA using novel procedure for preparation of hydroxyindoles
Muratake, Hideaki,Matsumura, Naoshige,Natsume, Mitsutaka
, p. 559 - 571 (2007/10/03)
An asymmetric total synthesis of natural (+)-duocarmycin SA (1) starting from L-malic acid (7) was achieved as shown in Chart 5, establishing firmly the absolute configuration of 1. In order to find suitable reaction conditions for the key step, i.e., the formation of an alkoxyindole derivative, model compounds 9 and 40 were synthesized and two acetalization conditions using i) 2-ethyl-2-methyl-1,3-dioxane and boron trifluoride etherate, and ii) 1,3-bis(trimethylsilyloxy)propane and trimethylsilyl trifiate were found to be effective. The former conditions were successfully applied to the total synthesis and 49b was prepared from 48 in 54% yield. Further elaborations including i) Curtius rearrangement of 53b to 56, and it) cleavage of the primary benzyloxy group in the presence of the secondary one in its close vicinity (56→57) led to the relay compound 62, whose conversion to 1 has already been accomplished.
Stereoselective Additions of Chiral, Functionalized Organozinc Reagents to Achiral and Chiral Aldehydes: a Matched-Mismatched Case in Organozinc Chemistry
Koert, Ulrich,Wagner, Holger,Pidun, Ulrich
, p. 1447 - 1458 (2007/10/02)
The additions of the enantiomerically pure organozinc reagents 17 and 33 to the THF-aldehyde 1 in the presence of the monodentate Lewis acid boron trifluoride-ether give the nonchelation-controlled addition products 7 and 36, respectively (stereoselectivity 95:5, 86:14).These results provide a route to oligo(tetrahydrofuran)s with the relative stereochemistry trans-syn-cis.A stereodirecting effect of the chiral center in the organozinc reagent 17 is found, leading to simple diastereoselectivies in the reaction with achiral aldehydes and to a matched-mismatched case in the reaction with the chiral aldehyde 1. - Key Words: Addition, stereoselective, nonchelation-controlled / Reagent, organozinc / Stereodifferentiation, double / Oligo(tetrahydrofuran)
