Transition metal-mediated routes to cyclopentenones

3,5-Bis-(trifluoromethyl)phenyl sulfones in the synthesis of 3,5-disubstituted cyclopent-2-enones

“…The organic phase was further washed with a saturated solution of Na 2 SO 3 (3 x 50mL) and NaHCO 3 (2 x 50 mL). The organic phase was dried (MgSO 4 ), and after solvent evaporation the corresponding crude oxiranes were obtained as a mixture of diastereomers (see Scheme 3), which were purified by flash chromatography (hexane/EtOAc) to afford pure compounds 5 (14), 161 (23), 145 (29), 135 (23), 133 (16), 109 (17), 83 (15), 82 (20), 81 (100), 65 (14), 53 (17) . General procedure for epoxide opening with benzylamine.…”

“…In the α,α-dialkylation of BTFP sulfone 1b a 28% yield of the cyclopentenol 4 was also obtained as a consequence of a nucleophilic substitution of the sulfonyl group by the base. On the other hand, K 2 CO 3 was the base which gave the best yields for the α,α-dialkylation reaction of the more acidic sulfones 1c-e, affording the corresponding adducts 3c-e in yields between 60 and 76% (Table 1, entries [3][4][5]. It is worth mentioning that non-activated benzyl sulfones require much stronger bases, such as n-BuLi at 0ºC, to perform this α,α-dialkylation process with (Z)-1,4-dichlorobut-2-ene.…”

“…Among them we can mention classical routes such as the base-catalyzed intramolecular aldol condensation of 1,4-dicarbonyl compounds, 1 the intramolecular Wittig-type reactions, 2 intramolecular 1,5-C-H insertions, 3 and the Nazarov 4 cyclization. Moreover, different transition metal-mediated approaches 5 such as the Pauson-Khand reaction, 6 and the Rautenstrauch rearrangement, 7 have become very popular for the synthesis of this type of compounds. We have recently shown that the 3,5-bis-(trifluoromethyl)phenyl (BTFP) group is a strong electron-withdrawing group, and that the corresponding BTFP sulfonyl group is an excellent nucleofuge in base-promoted β-elimination processes used in the stereoselective synthesis of Eaconitates by dialkylation under phase-transfer-catalyzed conditions followed by concomitant elimination 8 ( Figure 2).…”

Cationic cobalt(I) catalysts for the asymmetric cyclocarbonylation of 1,6-enynes

“…The [2+2+1] cycloaddition of an alkyne, an alkene, and CO promoted by octacarbonyldicobalt as the stoichiometric reagent (Pauson-Khand reaction) is a very important reaction for the synthesis of cyclopentenones. 1,2 This is even more evident after the reaction was carried out catalytically and after the catalytic activity of various metal systems was determined. 3 Furthermore, research devoted to the development of efficient asymmetric catalysis has been reported.…”

Regio‐ and Stereoselective Synthesis of Cyclopentenones: Intermolecular Pseudo‐Pauson–Khand Cyclization

“…Regarding the popular Pauson-Khand reaction, even though the intramolecular process is recognized as the most efficient access to fused cyclopentenones, there are significant drawbacks in the case of the intermolecular reaction, the major one being the necessity of using highly reactive or strained alkenes. [6,7] In contrast, advances have been made to replace the highly toxic carbon monoxide with more friendly CO sources like aldehydes. [8] Importantly, the asymmetric version of these processes still requires additional development.…”