Formation of Condensed 1H-Pyrrol-2-ylphosphonates and 1,2-Dihydropyridin-2-ylphosphonates via Kabachnik–Fields Reaction of Acetylenic Aldehydes and Subsequent 5-exo-digor 6-endo-digCyclizations

Abstract

Kabachnik-Fields reactions of various carbocyclic or heterocyclic acetylenic aldehydes together with subsequent Lewis acid catalyzed cyclizations have been studied. It was found that 5-exo-dig versus 6-endo-dig cyclization mode strongly depends on the structure of starting materials. Thus, nonaromatic acetylenic α-anilinomethylphosphonates underwent gold(III)-catalyzed or iodine-mediated 5-exo-dig cyclization to 1H-pyrrol-2-ylphosphonates. In contrast, electron-withdrawing heteroaromatic substrates formed 1,2-dihydropyridin-2-ylphosphonate ring containing materials via an exclusive 6-endo-dig ring-closure process. The dual mode of cyclization is possible only for α-amino (2-alkynylphenyl)methylphosphonates containing a benzene ring.

Efficient Synthesis of 5‐Chalcogenyl‐1,3‐oxazin‐2‐ones by Chalcogen‐Mediated Yne–Carbamate Cyclisation: An Experimental and Theoretical Study

“…Various N-Cbz-protected propargylic amines 1 bearing different aromatic and aliphatic groups attached to the alkyne moiety afforded the corresponding products 2 in excellent yields in the most cases (Table 1, entries 5-7); although the aryl-substituted starting materials 1e,f afforded the corresponding phenylselenylated cyclisation products in excellent yields (96-99 %), the 2-phenylethyl-substituted 1g only gave a moderate yield (71 %). [a] Reagents and conditions: 1 (0.1 mmol), phenylselenyl chloride (0.15 mmol), acetonitrile (2.5 mL, entries 1-7); 1 (0.1 mmol), phenylsulfenyl chloride in 1,2-dichloroethane (0.4 m, 0.15 mmol), acetonitrile (2.5 mL, entries 8-13); 1 (0.1 mmol), phenyltellanyl bromide in 1,2-dichloroethane (0.5 m, 0.15 mmol), acetonitrile (2.5 mL, entries [14][15][16][17][18][19].…”

“…Finally, N-Cbz-protected propargylic amines 1 dissolved in acetonitrile were treated with a freshly prepared 0.5 m solution of phenyltelluryl bromide in 1,2-dichloroethane. [25] These yne-carbamate cyclisation reactions required longer times and provided the 5-phenyltellanyl-1,3-oxazin-2-ones 4 in moderate-to-high yields (58-87 %; Table 1, entries [14][15][16][17][18][19]. The cyclisation of propargylic amines derived from benzaldehyde and p-tolylaldehyde yielded the corresponding products in good yields (75-87 %; Table 1, entries 14 and 15).…”

“…Several authors have proved that both cyclisation modes are possible in reactions carried out on related substrates, and have shown that the regioselectivity of the reaction depends on the structure of the starting material and the nature of the reagent or catalyst. [18][19][20][21][22] Scheme 1. Electrophilic yne-carbamate chalcogen-cyclisation of N-Cbz-protected propargylic amines.…”

6. Synthesis of α-aminophosphonates by the Kabachnik–Fields reaction and by the Pudovik reaction

“…The three-component condensation of amines, 2-alkynylindole-3-carbaldehydes and dimethyl phosphite was carried out applying a catalytic amount of BF 3 •OEt 2 as a Lewis acid catalyst ( Figure 6.7) [40].…”

Silver comes into play: Henry reaction and domino cycloisomerisation sequence catalysed by [Ag(i)(Pc-L)] complexes

“…The solvent was then evaporated under reduced pressure and the crude material was puried by ash chromatography over a silica gel column with gradients of n-hexane/ethyl acetate as eluent. 2-Alkynylbenzaldehydes 10a, 61 b, 61 c, 81 d, 61 and e, 61 and 2-alkynylnicotinaldehydes f 82 and g 83 are known compounds. They were…”