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ISBN-10: 3131016248

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Additional info for Methoden der organischen Chemie vol.E9e Hetarenes III, Part 5 Index

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28). Esterification of 240 followed by N-tert-BOC protection and DIBALH reduction provided aldehyde 244 (X = O) which was subjected to Wittig olefination. Introduction of a two carbon aldoxime chain on N in 244 (X = CH2) was carried out by alkylation with Et a-bromoacetate after deprotection of the N atom in 244. Reduction and oximation led to 245. (28) Although the thermal IOOC reactions can sometimes be accomplished at 80 °C [64], the oxime olefins 242a–d and 245a, b required heating in toluene at 180 °C in a sealed tube.

The silyl nitronate 161, generated in situ, underwent smooth ISOC reaction to the N-trimethylsilyloxyisoxazolidines 162. Attempted desilylation of 162a with aqueous HCl or anhydrous CF3CO2H followed by liberation of the salt provided a 3:1 mixture of hydroxy oxime 163a and isoxazoline 164a (see Table 15). While acid catalyzed elimination of Me3SiOH from 162a provides isoxazoline 164a, base treatment to liberate the amine after acidification causes partial ring cleavage to oxime 163a. Apparently, only a single isomer (trans) was observed for both 163a and 164a.

This ring closure proceeded stereospecifically to generate three adjacent stereogenic centers. LAH reduction of 246b resulted in isolation of stereospecifically functionalized tetrahydrofuran derivative 247b in 75% yield. 2 Role of Substituents in the Oxime-(H)-Nitrone Isomerization From the above, it is interesting to note that while the temperature required to effect IOOC of an oxime possessing amine N is 80 °C and an oxime possessing ether O is 110 °C, it is much higher (190 °C) for corresponding C compounds.

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Methoden der organischen Chemie vol.E9e Hetarenes III, Part 5 Index by Houben-Weyl


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