90270-52-3Relevant academic research and scientific papers
First successful metal coordination control in 1,3-dipolar cycloadditions. High-rate acceleration and regio- and stereocontrol of nitrile oxide cycloadditions to the magnesium alkoxides of allylic and homoallylic alcohols
Kanemasa, Shuji,Nishiuchi, Masaki,Kamimura, Akio,Hori, Kenzi
, p. 2324 - 2339 (2007/10/02)
The first successful control of stereo- and regioselectivity in 1,3-dipolar cycloadditions by metal coordination is described. The presence of magnesium ions dramatically accelerates nitrile oxide dipolar cycloadditions to allylic alcohols, improving both the regio- and stereoselectivity of the reaction. For example, cycloadditions to terminal allylic alcohols bearing α-chirality produce syn-stereoisomers of 2-isoxazolines selectively, and reactions involving the magnesium alkoxides of internal allylic alcohols are exclusively regioselective in favor of 5-hydroxymethyl-2-isoxazolines. Metal alkoxides other than magnesium, such as lithium, zinc, and aluminum alkoxides, are less effective. These reactions involve the formation of activated intermediates in which a nitrile oxide and an allylic alkoxide coordinate to the magnesium ion. Theoretical calculations indicate that the formation of the coordinated intermediates enhances the rate of cycloaddition and also improves the syn-selectivity.
Nucleophilic Additions to and Reductions of 5-Formyl- and 5-Acyl-2-isoxazolines (4,5-Dihydroisoxazoles): A Stereoselective Route to β,γ-Dihydroxy Ketones
Curran, Dennis P.,Zhang, Jiancun
, p. 2613 - 2625 (2007/10/02)
Reductions of readily available 5-acyl-2-isoxazolines with L-Selectride follow the Felkin-Anh model and produce syn-5-hydroxyalkyl-2-isoxazolines with excellent (>95:5) selectivities.Swern oxidation of 5-hydroxymethyl-2-isoxazolines, followed by direct ad
Generation of nitrile oxides through O-metalation of hydroximoyl chlorides. Chelation-controlled syn-selective cycloaddition of nitrile oxides to α-substituted allyl alcohols
Kanemasa, Shuji,Kobayashi, Shigeru,Nishiuchi, Masaki,Yamamoto, Hidetoshi,Wada, Eiji
, p. 6367 - 6370 (2007/10/02)
New generation of nitrile oxides by treatment of hydroximoyl chlorides with organometallics is reported. Their cycloadditions to the allyl alcohols bearing a chiral center at the 1-position proceed in a syn-selective manner, providing the first example of
Diastereofacial Selection in Nitrile Oxide Cycloaddition Reactions. The Anti-Directing Effect of an Allylic Oxygen and Some New Results on the Ring Metalation of Isoxazolines. A Synthesis of (+/-)-Blastmycinone
Kozikowski,, Alan P.,Ghosh, Arun K.
, p. 2762 - 2772 (2007/10/02)
The extent of diastereoselectivity associated with the reactions of nitrile oxides with alkenes bearing an allylic oxygen substituent has been studied.Reasonable levels of such diastereoselectivity have been found when the tert-butyldimethylsilyl ether derivative of 3-buten-2-ol (5) or (+)-(S)-isopropylidene-3-butene-1,2-diol (1) are employed as dipolarophiles.The stereochemical course of these cycloaddition reactions has been proven rigorously through the transformation of the adducts to known γ-lactones.The stereochemistry associated with the metalation/alkylation of 5-alkoxymethyl-substituted isoxazolines has also been probed in order to further expand the use of these heterocycles as aldol equivalents in natural products total synthesis.A synthesis of (+/-)-blastmycinone (34) is reported which combines the two foregoing aspects of stereocontrol.The levels of regio- and stereoselectivity found in the cycloaddition reactions of the cis- and trans-disubstituted alkenes 35 and 39 prepared from isopropylidene-D-glyceraldehyde are also discussed.A single example of the reaction of a chiral alkene with a chiral nitrile is presented.
