A new cascade ring enlargement of isoxazolidines formed from 2-chloro-2-cyclopropylideneacetates

Chameleon Thermal Behavior of Cycloadducts of Nitrones to Methyl 2-Chloro-2-cyclopropylidene- and 2-Chloro-2-spiropentylideneacetates

“…However, by heating 13 and 14 in the more polar DMSO at 100 °C, a clean and fast reaction occurred to give the hexahydroindolizin-5-ones 34 12 and 35 in 83 and 73% yield, respectively (Scheme ) . As these compounds were present only in minute amounts in the heated toluene solutions, it is obvious that the polarity of the solvent plays a key role in controlling the rearrangement process.…”

Synthesis of Enantiopure Indolizinones by Cascade Ring Enlargements of 4‘-Chlorospiro[cyclopropane-1,5‘-isoxazolidines]

“…Although compounds 4 ( n = 0, 1) without the additional alkoxy substituent, upon heating in DMSO at 100 °C, were cleanly transformed into the corresponding indolizinones 6 (Scheme ), the cycloadducts 12a,b under these conditions underwent decomposition only (Table , entry 1), and the same happened with the cyclobutane derivative 14a under the same conditions. Since the final rearrangement was supposed to be triggered by the abstraction of the bridgehead proton by a nucleophile, the more severe steric encumbrance caused by the large tert -butoxy group in 12a,b and 14a could hamper this process.…”

“…Whereas their thermal rearrangement to produce tetrahydropyridones has found wide application in the synthesis of natural compounds or nonnatural analogues, only recently has the use of acidic conditions or the catalysis by Pd(II) salts revealed the possibility to also produce β-lactams and dihydropyridones, respectively. Another novel reaction mode has previously been reported for the cycloadducts 4 obtained from nitrones 3 and methyl 2-chloro-2-cyclopropylideneacetates 1 and 2 . − This reactivity depended largely on the substrate and varied greatly with the nature of the substituents on the isoxazolidine. The most promising result was the observed rearrangement of the adducts 4 into the corresponding indolizinone derivatives 6 (Scheme ).…”

“…Another novel reaction mode has previously been reported for the cycloadducts 4 obtained from nitrones 3 and methyl 2-chloro-2-cyclopropylideneacetates 1 and 2. [8][9][10] This reactivity depended largely on the substrate and † Università di Firenze. ‡ Georg-August-Universität Göttingen.…”

“…Another novel reaction mode has previously been reported for the cycloadducts 4 obtained from nitrones 3 and methyl 2-chloro-2-cyclopropylideneacetates 1 and 2. [8][9][10] This reactivity depended largely on the substrate and varied greatly with the nature of the substituents on the isoxazolidine. The most promising result was the observed rearrangement of the adducts 4 into the corresponding indolizinone derivatives 6 (Scheme 1).…”