Pentannulation of N-heterocycles by a tandem gold-catalyzed [3,3]-rearrangement/Nazarov reaction of propargyl ester derivatives: a computational study on the crucial role of the nitrogen atom

• Giovanna Zanella,
• Martina Petrović,
• Dina Scarpi,
• Ernesto G. Occhiato and
• Enrique Gómez-Bengoa

Beilstein J. Org. Chem. 2020, 16, 3059–3068, doi:10.3762/bjoc.16.255

• theoretical calculations predict that the position of the propargylic acetate substituent has a great impact on the reactivity. In contrast to our previous successful cyclization of the 2-substituted substrates, where the nitrogen favors the formation of the cyclized final product, the substitution at

Recent applications of the divinylcyclopropane–cycloheptadiene rearrangement in organic synthesis

• Sebastian Krüger and
• Tanja Gaich

Beilstein J. Org. Chem. 2014, 10, 163–193, doi:10.3762/bjoc.10.14

• apply the transition metal catalyzed 1,2-acyl shift with subsequent vinyl carbenoid formation. Propargylic acetate 251 (see Scheme 33) has been shown to undergo 5-exo-dig cyclization via 252 to give zwitterionic intermediate 253. A concomitant fragmentation reaction yielded vinyl-carbenoid 254. Uemura

• and coworkers used this chemistry with propargylic acetate 255 to achieve cyclopropanation with various dienes, for example cyclopentadiene, to generate a cis/trans-mixture of divinylcyclopropanes 256. Heating of this mixture of compounds resulted in the formation of bridged tricycle 257 in good yield

• wise mechanism and involves charged intermediates. Nevado and coworkers [206] applied a closely related reaction to propargylic acetate 262 using a cationic gold(I) catalyst, which was used to selectively cyclopropanate the less hindered double bond of dienes like 263. Spontaneous DVCPR provided

Gold-catalyzed regioselective oxidation of propargylic carboxylates: a reliable access to α-carboxy-α,β-unsaturated ketones/aldehydes

• Kegong Ji,
• Jonathan Nelson and
• Liming Zhang

Beilstein J. Org. Chem. 2013, 9, 1925–1930, doi:10.3762/bjoc.9.227

• -unsaturated ketones/aldehydes. Results and Discussion We began by subjecting the propargylic acetate 4a to the suitable conditions developed in our previous study, namely IPrAuNTf2 (5 mol %) and 8-methylquinoline N-oxide (3, 1.5 equiv) in 1,2-dichloroethane at ambient temperature. To our delight, the reaction

• approach. Gold-catalyzed regioselective oxidation of a sterically biased internal alkyne. Gold-catalyzed oxidation of the propargylic acetate 4a and the mechanistic rationale. A drastically different outcome by using diphenyl sulfoxide as the oxidant. Reaction scope studies for the formation of α

Complete transfer of chirality in an intramolecular, thermal [2 + 2] cycloaddition of allene-ynes to form non-racemic spirooxindoles

• Kay M. Brummond and
• Joshua M. Osbourn

Beilstein J. Org. Chem. 2011, 7, 601–605, doi:10.3762/bjoc.7.70

• temperatures (Table 1, entry 1) and the substrates containing –OMe and –OAc leaving groups were unreactive toward the lower order cuprates (Table 1, entries 2–5). The optimal conditions were found using the propargylic acetate and the higher order cuprate, t-Bu2Cu(CN)Li2 at −78 °C which gave compound 8 (R

• resembling compound 2, gave the racemic spirooxindole product. This finding will be discussed in detail in a full account of this work. To examine the chiral transfer from the propargylic acetate 7 to the allenyloxindole 8, a chiral 1H NMR shift analysis was performed using (+)-Eu(hfc)3. The NMR spectra of

A thermally-induced, tandem [3,3]-sigmatropic rearrangement/[2 + 2] cycloaddition approach to carbocyclic spirooxindoles

• Kay M. Brummond and
• Joshua M. Osbourn

Beilstein J. Org. Chem. 2010, 6, No. 33, doi:10.3762/bjoc.6.33

• observed, but are likely intermediates of an infrequently encountered thermal [3,3]-sigmatropic rearrangement of a propargylic acetate. Keywords: allene; propargylic acetate; spirooxindole; thermal [2 + 2] cycloaddition; thermal [3,3]-sigmatropic rearrangement; vinylidene indolin-2-one; Introduction

• 5 could be obtained by way of a thermal [3,3]-sigmatropic rearrangement of the propargylic acetate 6 to give compound 5 where R2 = OAc (Figure 2) [27]. Preparation of propargylic acetate 9a was accomplished by the addition of the lithium acetylide of 8 to N-methyl isatin (7) followed by acetylation

• of the resulting propargyl alcohol. Heating propargylic acetate 9a to 225 °C in 1,2-dichlorobenzene in the microwave for 30 min gave the spirooxindole 10a in 60% yield (Scheme 2). Structural confirmation of 10a was achieved using COSY, HMQC and HMBC. Attempts to effect the [3,3]-sigmatropic