Absolute configuration determination of theanti-head-to-head photocyclodimer of anthracene-2-carboxylic acid through cocrystallization withL-prolinol

Abstract

The absolute configuration has been established of the enantiopure anti-head-to-head cyclodimer of anthracene-2-carboxylic acid (AC) cocrystallized with L-propinol and dichloromethane [systematic name: (S)-2-(hydroxymethyl)pyrrolidin-1-ium (5R,6S,11R,12S)-8-carboxy-5,6,11,12-tetrahydro-5,12:6,11-bis([1,2]benzeno)dibenzo[a,e][8]annulene-2-carboxylate dichloromethane monosolvate], C5H12NO(+)·C30H19O4(-)·CH2Cl2. In the crystal structure, the AC dimer interacts with L-prolinol through a nine-membered hydrogen-bonded ring [R2(2)(9)], while the dichloromethane molecule is incorporated to fill the void space. The absolute configuration determined in this study verifies a recent assignment made by comparing theoretical versus experimental circular dichroism spectra.

Supramolecular Photochirogenesis with a Higher-Order Complex: Highly Accelerated Exclusively Head-to-Head Photocyclodimerization of 2-Anthracenecarboxylic Acid via 2:2 Complexation with Prolinol

“…As shown in Table (runs 11–14), the photocyclodimerization of A in the presence of P (1–10 equiv) at 0 °C was accelerated by a factor of 1.7–4.6 in apparent rate, relative to free A (run 2), to afford the HH dimers in 95–98% selectivity and 3 – in 39–43% ee. The preferential formation of 3 – with P -absolute configuration agrees with the favored re-re conformer in A 2 · P 2 (Figure ). The rate enhancement, the exclusive formation of HH dimers, and the steady HH selectivity and ee value observed at P / A ≥ 1 are reasonably accounted for in terms of the intracomplex photocyclodimerization of A 2 · P 2 .…”

“…In the 1:1 complex of A with T , the N -ethylprolinol moiety of T captures A by forming a nine-membered hydrogen-bonding network, while the benzamide moiety preferentially shields the enantiotopic si face of A to afford the P -enantiomer of 3 in up to 49% ee upon attack from the exposed re face by free A or A · T in the excited state. ,, It is likely therefore that any template that lacks the shielding fence leads to poor enantioselectivity. Indeed, hydrogen-bonding template TM166, which is epimeric to T at the prolinol’s 4-position and hence favors the extended conformation, gave racemic 2 and 3 .…”

“… a Irradiation of A (0.25 mM, unless noted otherwise) performed in CH 2 Cl 2 at λ > 320 nm in the presence and absence of prolinol derivative ( P , P NM , or P OM ) under N 2 . b Consumption of A determined by monitoring the UV/vis spectral change at 390 nm and the relative rate compared with the photocyclodimerization of free A at 25 °C, estimated by dividing the conversion by the irradiation time (calculated only for low-conversion runs to estimate the initial rate). c Population of free A and A · P complexes calculated by extrapolating the association constants shown in Tables and . d The negative sign for the ee value indicates preferred formation of ( P )- 3 ( 3 – ); error in yield = ±1%; error in ee = ±3%. e HH = ( 3 + 4 )/( 1 + 2 + 3 + 4 ). f Conversion not comparable with the other data due to the partial precipitation of A at −25 °C in the absence of P . g Not determined due to low chemical yield. h [ A ] = 0.1 mM. i [ A ] = 0.01 mM due to low solubility. j Not determined. …”

“… d The negative sign for the ee value indicates preferred formation of ( P )- 3 ( 3 – ); error in yield = ±1%; error in ee = ±3%. …”

Enantioselective [4+4] photodimerization of anthracene-2,6-dicarboxylic acid mediated by a C2-symmetric chiral template

“…Compound 3 is an achiral meso-compound. In contrast to the enantioselective [4+4] photodimerization of anthracene-2-carboxylic acid, which has been extensively studied in recent years, 4 there have been relatively few investigations on the photodimerization of 1. In a fundamental circular dichroism (CD) study, the absolute configuration of compounds 2 and ent-2 was determined, which allows their unambiguous assignment based on their chiroptical data, e.g.…”