Synthesis of Heterocyclic Systems by Transition‐Metal‐Catalyzed Cyclization‐Migration Reactions – A Diversity‐Oriented Strategy for the Construction of Spirocyclic 3(2H)‐Furanones and 3‐Pyrrolones

Abstract

Two platinum(II)-catalyzed heterocyclization-migration reactions that provide five-membered heterocycle products are described. With 5 mol-% of PtCl 2 as a catalyst, 2-alkynyl-2-hydroxy carbonyl compounds 1 are converted into 3(2H)-furanones 2 at 80°C in moderate to excellent yields under very mild reaction conditions. The reaction is proposed to proceed through an oxonium ion intermediate B, which triggers a stereospecific 1,2-shift analogous to an α-ketol rearrangement. When exploited in a different manner, the 2-alkynyl-2-hydroxy carbonyl compounds 1 afford 3-pyrrolones 3 in 33-81 % yield. For this purpose, the starting compounds 1 are

The CLIP/CLAP-HSQC: Pure absorptive spectra for the measurement of one-bond couplings

“…An example is shown in Fig. 5 for a methylene group of 6-methyl-2-phenyl-1-oxa-spiro [4,4]non-2-en-4-one [34,35]. The two cross peaks in this case could be resolved by either changing the spectrometer frequency or e.g.…”

“…CLIP and CLAP-HSQC spectra of a methylene group of 6-methyl-2-phenyl-1-oxa-spiro[4,4]non-2-en-4-one[34,35] dissolved in CDCl 3 and recorded at 600 MHz proton frequency (a). After combining the two spectra in IPAP manner (b), coupling constants of the overlapped signals can be determined from the corresponding a and b subspectra (c).…”

Gold‐Catalyzed Migrations and Ring Expansions

“…As such, spirocycles can be efficiently prepared from homopropargyl ketones through a gold-catalyzed cyclization/alkyl migration process as shown in Scheme 37 76,77 . Examples of the attack of heteroatoms other than oxygen onto gold-activated alkynes in order to trigger alkyl migrations have also been described.…”

2‐Iodoxybenzoesäure – ein einfaches Oxidationsmittel mit einer Vielfalt an Anwendungsmöglichkeiten

“…Oxidation von 2-Benzopyriliumsalzen. [185] Schema 49. a-Hydroxylierung von Carbonylverbindungen nach Kirsch et al [188,189] Schema 50. Effekt von Yb(OTf) 3 als Additiv.…”