Photodimerization of coumarins in micelles: limitations of alignment effect

Abstract

Longicaudatine has strong reserpine-like activity, which is different from the activities described by Sandberg et al.18 for fractionated extracts of S. longicaudata. Experimental SectionLongicaudatine (1): mp 350 °C dec; [a]D +141°( c 0.5, CHC13); UV 223 nm (log t 4.66), 270 (sh), 284 (4.28), 290 (4.26), 307 (sh, 3.97); in perchloric acid a strong absorption maximum appears at 268 nm; IR (KBr) 3420, 2900,1630,1600,1480, 740 cm"1. The 400-MHz 1H NMR spectrum was recorded in CDC13 on material containing 0.25 molecule of acetone of crystallization (Table I). 13C NMR spectra were recorded at 62 and 25.15 MHz, in CDC13. Proton-noise-decoupled, off-resonance-decoupled, and selective decoupled (¿ 9.6,6.06, and 4.27 in the NMR spectrum) spectra were determined (see Table II). On TLC plates a blue color is obtained with the spray reagents 0.2 M iron(III) chloride in 35% aqueous perchloric acid and 1% cerium(IV) sulfate in 10% aqueous sulfuric acid.

Macroscalar Helices Co‐Assembled from Chirality‐Transferring Temperature‐Responsive Carbohydrate‐Based Bolaamphiphiles and 1,4‐Benzenediboronic Acid

“…The chemical shifts belonging to the cyclobutane protons and cyclobutane methyl protons were visible at 3.41 and 1.41 ppm (see Supporting Information for 1 H NMR spectra). 1 H NMR spectra further confirmed the formation of primarily the syn head–tail product with minor quantities of the anti head–tail conformation, which is in agreement with previous reports [23, 24] …”

Supramolecular Control of the Template‐Induced Selective Photodimerization of 4‐Methyl‐7‐O‐hexylcoumarin

“…[8] The transition moments can further be influenced by solvent polarity [11] and the use of cyclodextrin or micelles. [12,15,16] With respect to previous reports, [30±34] we set forth the design and subsequent synthesis of a template, which Scheme 1. Schematic representation of the reaction pathway responsible for selective syn photodimer formation within a supramolecular 2:1 species.…”

“…Under typical experimental conditions, however, the two syn (2 A and 2 B) photoproducts are formed predominately, while only trace amounts of the anti dimers 2 C and 2 D are observed. [7] The ratio of coumarin photoproducts can significantly be altered through control of the reaction conditions such as solvent choice, [9,11,12] Lewis acid addition, [13,14] micellar environment, [15,16] solid-state irradiation, [13,14] modification of the coumarin precursor, [17,18] use of inclusion complexes [15] and tethered precursors, [17, 19±21] or recently with pseudo-rotaxanes. [22] Much effort has been focused on crystal engineering and packing within the solid state to influence the product distribution.…”

“…The configuration of the observed photodimers is consistent with previous reports for sensitized dimerization. [15,16,19,20] No appreciable change was observed when performing either direct irradiation in chloroform or sensitized irradiation with acetone. Since the experimental conditions employed are relatively dilute, direct excitation of the precursor undergoes intersystem crossing forming the triplet state before quenching occurs.…”

Water-soluble octa acid capsule as a reaction container: Templated photodimerization of indene in water

“…[1] For this purpose, various media such as zeolites, clays, crystals, cyclodextrins, cucurbiturils, calixarenes, micelles, dendrimers, polymers, host-guest complexes and natural proteins have been successfully explored during the last few decades. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] These studies have clearly shown that the confinement and weak interactions provided by a host can steer reactivity of guest molecules resulting in highly selective reactions that are otherwise challenging in isotropic media. Reactions of a guest molecule in confined spaces could be visualized to occur within a 'reaction cavity' with a defined boundary and some amount of 'free space' surrounding the reactant within the cavity.…”