Ongoing efforts have been dedicated to the development of reaction processes controlled by chiral hypervalent iodine reagents with high enantioselectivity. [1][2][3][4][5][6][7][8][9][10][11][12] The oxidation of sulfides into sulfoxides, [2] the a-oxygenation of ketones, [3,4] the dioxygenation of alkenes, [4,5,12] and the dearomatization of phenols [6-8, 9b] have been reported, and most of these reactions resulted in an encouraging level of enantioselectivity. Kita and co-workers reported dearomatizing spirolactonization of naphthols (78-86 % ee) using a spirocyclic iodine(III) reagent.[6] Ishihara and co-workers recently reported that higher enantioselectivities were obtained for the spirolactonization by using a chiral iodine compound derived from lactic acid. [8] Our studies with optically active hypervalent iodine compounds have been focused on mechanisms of the reaction concerned [11] as well as synthetic applications.[12] Asymmetric oxidation of 4-acyloxybut-1-ene into 3-acyloxytetrahydrofuran (up to 64 % ee) was achieved by using chiral hypervalent iodine(III) reagents, 1 and 2, which have a lactate moiety as a chiral source.[12] During the course of these studies for the asymmetric oxidative cyclization of alkenes, we found that oxidation of ortho-alk-1-enylbenzoate with the hypervalent iodine reagent regio-and diastereoselectively gave 3-alkyl-4-oxyisochroman-1-one in a practically useful degree of enantiomeric purity (90-98 % ee); the isochromanone framework is a biologically relevant building block of natural products. [13,14] Herein, we report the synthetic utility of such enantiodifferentiating endo-selective oxylactonizations.The series of optically active hypervalent iodine (III) reagents 1-6 employed in this report is shown in Scheme 1. On the basis of reagents 1 and 2 reported previously, [12] the structures of the iodine reagents were tuned for improved enantioselectivity. The X-ray crystallographic structures of 1-4 showed a typical T-shape orientation around the iodine center, where the two acetoxy ligands occupied apical positions (see the Supporting Information).2-Ethenylbenzoic acid (7 a) was subjected to the reaction conditions with the optically active hypervalent iodine(III) reagent. The reaction was carried out in the presence of paratoluenesulfonic acid (TsOH) to activate the iodine reagent, and the tosylate also worked as a nucleophile to give lactones 8 a and 9 a ( Table 1). The reaction proceeded regioselectively to give the d-lactone product 8 a as the major product. The reaction with 6 gave a higher ee value of 8 a with high regioselectitvity (Table 1, entry 5).It is remarkable that the oxylactonization proceeds with endo selectivity [15,16] in addition to the high enantioselectivity. For elucidation of the mechanism of the endo selectivity and its synthetic applications, we varied the nucleophile and the substrate in the oxylactonization. When boron trifluoride diethyl etherate was employed as an activator in the presence Scheme 1. Optically active hypervalent iodine(III) rea...

Erfolg mit Lactat: Die asymmetrische Synthese von 3‐Alkyl‐4‐oxyisochroman‐1‐on gelingt durch die Titelreaktion mit einer Serie optisch aktiver hypervalenter Iod(III)‐Reagentien, die aus Lactat oder Valin als chiraler Quelle präpariert wurden. Die Oxylactonisierung ist hoch regio‐, diastereo‐ und enantioselektiv.

Described are the syntheses, crystal structures, and solid-gas adsorption behaviors of azacalix[4]arene tetramethyl ether and azacalix[5]arene pentamethyl ether. While the former compound exhibited no adsorption of four main atmospheric components, the latter selectively and rapidly adsorbed CO(2) at ambient temperature and pressure. X-ray crystallographic and potential energy distribution analysis revealed that azacalix[5]arene created an energetically favorable space for CO(2) in its seemingly nonporous crystal, leading to the observed selective CO(2) uptake under ambient conditions.

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The present protocol is applied to the synthesis of the naturally occurring aromatase inhibitor (VII).