Base-Catalyzed [3 + 2] Cycloaddition ofN-Benzyl Ketimines to Arylacetylenes Followed by Oxidation: A One-Pot Access to Polyarylated 2H-Pyrroles via Intermediate Pyrrolines

Abstract

Scheme 1. Previous Works Scheme 2. KOBu t /DMSO-Catalyzed [3 + 2] Cycloaddition of Ketimine 1a to Acetylene 2a Letter pubs.acs.org/OrgLett

Synthesis of 1-pyrroline derivatives via cyclization of terminal alkynes with 2-azaallyls

“…The cycliza-tion reaction was found to be highly sensitive to temperature. Decreasing the reaction temperature from 80 °C to room temperature also resulted in lower AYs (50-55%) or no reaction (entries [11][12][13]. When the ratio of 1a and 2b was adjusted to 1 : 1 or 1 : 2, the AY decreased to 67 or 60%, respectively (entries 14 and 15).…”

Regio- and stereoselective base-catalyzed assembly of 6-methylene-5-oxaspiro[2.4]heptanones from alkynyl cyclopropyl ketones

“…This results in lower acidity of alkynyl cyclopropyl ketones in comparison with classic alkynyl enolates, which implies the need to use stronger bases to activate the α-C–H bond. Therefore, we have chosen an inexpensive and easy-to-handle potassium tert -butoxide/DMSO catalytic system (p K a ∼ 32) 12 to activate the model ketone 1a . To our delight, when ketone 1a was treated with t -BuOK (10 mol%) in DMSO at room temperature for 120 min (Table 1, entry 1), the desired oxa-spirocyclopropane derivative 2a was obtained in 10% yield.…”

Modular approach to non-aromatic and aromatic pyrroles through gold-catalyzed [3 + 2] cycloaddition of 2H-azirines and ynamides

“…Moreover, the high synthetic potential of 3H-pyrroles, which have found application as hetero-dienes in the Diels-Alder reaction, has been convincingly proven. [21][22][23] In recent years, significant efforts have been made to construct 3H- [24][25][26][27][28] and 2H- 24,25,[29][30][31][32][33][34][35] pyrroles. Some of the reported synthetic schemes are based on the dearomatizations of 1Hpyrroles; typically, these reactions proceed under harsh conditions.…”

“…31,32 The cyclization of complex prefunctionalized substrates into 3H-and 2H-pyrroles requires a tedious assembly of the corresponding precursors. 29,34,35 To overcome these limitations, several modular synthetic methods have been proposed; however, they are either of a limited scope, 24,27,30 or employ inconvenient starting materials 25,26 (e.g., malodorous and toxic isocyanides 36 ). Considering all these data, one can conclude that the development of expedient modular protocols for the syntheses of these heterocycles comprises a challenging task.…”

“…In recent years, significant efforts have been made to construct 3 H - 24–28 and 2 H - 24,25,29–35 pyrroles. Some of the reported synthetic schemes are based on the dearomatizations of 1 H -pyrroles; typically, these reactions proceed under harsh conditions.…”