Serendipitous Observation of Liquid‐Phase Size Selectivity inside a Mesoporous Silica Nanoreactor in the Reaction of Chromene with Formic Acid

Abstract

An unprecedented product shape/size selectivity in the hydrolysis/decarboxylation reaction sequences of chromene with formic acid within MCM‐41 as a nanoreactor in the liquid phase is observed. Chromene is expected to form pyrimidine in the reaction with HCOOH. However, here, serendipitously, the product switches from pyrimidine to enol lactones and δ‐keto acids inside the nanoreactor. The shape/size selectivity in the liquid phase is a highly desired phenomenon in organic synthesis. We prepared four different varieties of porous silica materials to obtain this product selectivity. Very high yields of these biologically relevant compounds surpass that achieved by existing methodologies. Again, though there are few reports of coumarin‐fused enol lactones, this approach enables the easy synthesis of naphthalene‐fused enol lactones. Moreover, this is the first generalized synthesis of δ‐keto acids following a number of hydrolysis/decarboxylation/ring opening/tautomerization/decarboxylation steps.

Recyclable Mesoporous Organosilica Nanoparticles Derived from Proline-Valinol Amides for Asymmetric Organocatalysis

“…In spite of the potential of organically modified MSN, they have scarcely been applied in organocatalysis. Most of the examples involve simple achiral organocatalysts for aldol, − Knoevenagel, , and Henry condensations; ,,− Michael additions; cyanosilylation and Diels–Alder reactions; conversion of cellulose to 5-hydroxymethylfurfural; synthesis of tetrasubstituted imidazoles by a four-component reaction; selective formation of enol lactones and δ-keto esters from chromene and formic acid; and one-pot three-component synthesis of 2-aminochromene derivatives . As far as the asymmetric organocatalysis is concerned, only chiral imidazolidinones on mesoporous silica nanoparticles obtained by post-synthesis procedures have been described for stereoselective Diels–Alder cycloadditions …”

Designing Sites in Heterogeneous Catalysis: Are We Reaching Selectivities Competitive With Those of Homogeneous Catalysts?

“…For instance, a switch in selectivity has been reported, from the production of pyrimidine to enol lactones and δ-keto acids, when MCM-41 is used instead of other more conventional silica catalysts to promote the coupling of chromene with HCOOH. 1484 One particularly curious type of shape selectivity uses chiral mesoporous materials to introduce enantioselectivity in catalytic reactions. The synthesis of chiral mesoporous materials has constituted a challenge in itself, and is a field still in its infancy.…”

“…Because of the large dimensions involved, on the order of several nanometers, this idea has in general not proven viable, but there are nevertheless some notable exceptions. For instance, a switch in selectivity has been reported, from the production of pyrimidine to enol lactones and δ-keto acids, when MCM-41 is used instead of other more conventional silica catalysts to promote the coupling of chromene with HCOOH . One particularly curious type of shape selectivity uses chiral mesoporous materials to introduce enantioselectivity in catalytic reactions.…”

Visible Light-Driven Reductive Azaarylation of Coumarin-3-carboxylic Acids

“…4, 150.8 (2C), 148.7, 147.8, 130.5, 126.6, 125.8, 125.2, 122.8, 122.7 (2C), 40.6, 36.0 1,. 16 The pure product was isolated by flash chromatography on silica gel (n-hexane/ethyl acetate, 2:1) as a pale yellow oil in 41% yield (11.3 mg). 1 H NMR (700 MHz, chloroform-d) δ 8.53−8.51 (m, 2H), 7.92 (d, J = 9.1 Hz, 1H), 7.90−7.89 (m, 1H), 7.71 (dd, J = 8.5, 0.9 Hz, 1H), 7.51 (ddd, J = 8.5, 6.8, 1.4 Hz, 1H), 7.48 (ddd, J = 8.0, 6.8, 1.6 Hz, 1H), 7.37 (d, J = 9.0 Hz, 1H), 7.06 (ddd, J = 4.4, 1.6, 0.6 Hz, 2H), 4.94 (d, J = 6.7 Hz, 1H), 3.27 (dd, J = 16.0, 7.3 Hz, 1H), 3.18 (dd, J = 16.0, 1.8 Hz, 1H).…”