Experimental and Theoretical Evidence for Oxirane Formation Reaction of Pentacoordinate 1,2λ⁶-Oxathietanes with Retention of Configuration

Abstract

From our interest in diheteracyclobutanes 1 bearing highly coordinate main group elements at the neighboring position, 1,2 we have reported the synthesis and thermolysis of the pentacoordinate 1,2λ 6 -oxathietane 2. 3,4 Almost quantitative oxirane formation from 2 has suggested a possibility that the oxathietane is an intermediate of the Corey-Chaykovsky reaction of oxosulfonium ylides with carbonyl compounds. 3It has been proposed that the Corey-Chaykovsky reaction 5 involves the formation of an anti-betaine followed by a back side attack of an oxido anion on the -carbon. 6 But, if the oxathietane is a real intermediate of the Corey-Chaykovsky reaction, 7 S-O bond heterolysis followed by C-C bond rotation is necessary for such an oxirane formation. Electrostatic interaction between the oxido anion and the sulfonium cation, which seems a driving force of the formation of the oxathietane ring, would resist the C-C bond rotation. In this case, an alternative mechanism such as a concerted mechanism or a front attack of the oxido anion without the C-C bond rotation can be expected to be operative. In order to elucidate these possibilities, we have decided to examine the stereochemistry of the oxirane formation. In this paper we wish to report the first example of the oxirane formation with retention of configuration and the theoretical study of this process.Two diastereomers of pentacoordinate 1,2λ 6 -oxathietanes 3a and 3b with the Martin ligand 8 were synthesized by the same method as previously reported (Scheme 1). 3 The separation of diastereomers 6a and 6b was nicely performed by flash column chromatography (FCC, SiO 2 ). The stereochemistry of 8a and 8b was determined by differential NOE experiments as follows: NOE between a methine proton of carbon-3 and orthoprotons of the phenyl group of carbon-4 was observed for (3S,4R)-or (3R,4S)-8a and not for (3S,4S)-or (3R,4R)-8b. Since the stereochemistry around a pentacoordinate sulfur and the relationship between the SdO group and the phenyl group at carbon-3 for 3 are considered to be the same as those reported for 2 and, furthermore, the relative stereochemistry around carbon-3 and carbon-4 is retained during the oxidation of 8, 3a and 3b are concluded to have the structures as shown in Scheme 1.Thermolysis of 3a gave the corresponding oxirane 9a along with 5, phenyl-migrated ketone 10, benzaldehyde (11), cyclic sulfinate 12, a diastereomeric mixture of cyclic thioacetal S-oxides 13, and cyclic thioacetal 14 (Scheme 2). 9 In sharp contrast to the thermolysis of 2, 3 the yield of oxirane 9a was † Gifu University.(1) Kawashima, T.; Okazaki, R. Synlett 1996, 600-608. For pentacoordinate 1,2-oxaphosphetanes, see: Kawashima, T.; Kato, K.; Okazaki, R. In the formation reaction of spiropentanes by the reaction of sulfonium cyclopropylides with carbonyl compounds, a mechanism involving an oxathietane was proposed as an alternative one involving a ring expansion to a σ-sulfurane having an oxirane ring followed by reductive elimination of the sulfide, see: Bogdanowicz, M. J...

Syntheses, Crystal and Solution Structures, Ligand‐Exchange, and Ligand‐Coupling Reactions of Mixed Pentaarylantimony Compounds

“…The preparation of Tol 2 SbCl from Tol 3 Sb (16) and SbCl 3 (7) was tried repeatedly according to procedures described for Ph 2 SbCl. [28] However, we found that a large amount of byproducts such as TolSbCl 2 and Tol 3 SbCl 2 were always formed, so we were not able to isolate Tol 2 SbCl in pure form by recrystallization, although various solvents were examined.…”

“…The symmetry-forbidden apical-equatorial-coupling process has been reported once to be favored, [8] whereas recent calculations support the conclusion by Hoffmann that equatorial-equatorial coupling is the lowest energy process for PH 5 , AsH 5 , and SbH 5 , [9][10][11][12] although BiH 5 favors the apical-equatorial process. [11] Experimentally, the LCR of bis(biphenylene)methylphosphorane, [13] tetraaryltellurium, [14] 2-pyridylsulfuranes (generated in situ), [15] pentavalent oxathietane, [16] and pentavalent oxastibetane [17] have been reported, however, the essential nature of the selectivity of the LCR has yet to be discussed. We have already reported on the LCR of triarylbis(phenylethynyl)antimony(V) compounds for this purpose and found that no biaryls were formed from the LCR (Table 1).…”

Substituent Effects on the Stability and Antioxidant Activity of Spirodiazaselenuranes

“…Upon treatment of one equivalent of H2O2 with compound 36, a sharp peak was appeared at 863 ppm in the Se-NMR and mass spectral studies ( Figures S24-S27, SI). Sulfurane oxide and selenurane oxide with apical oxygen atoms are already known in the literature [17][18][19]. However, compound 38 is the first example of a stable selenurane oxide, which contains two nitrogen atoms at the axial positions.…”

“…However, the corresponding aromatic derivatives 6-7 were found to be much less active than the aliphatic compounds 4-5 [15,16]. Several sulfurane oxides and selenurane oxides such as 8-10, in which the chalcogen atoms are in the higher oxidation state, were also synthesized and isolated ( Figure 1) [17][18][19]. Although several example of spirodioxyselenuranes are available in the literature, examples of stable spirodiazaselenuranes are very rare.…”

Elucidation of the stereochemistry of thiirane formation from a 1λ4,2‐dithietane bearing two chiral carbon centers

“…The other is ligand dissociation to form a sulfonium salt followed by a nucleophilic attack on another ligand by the dissociated ligand. Although the ligand-coupling mechanism is common in the chemistry of hypervalent organosulfur compounds [1], some reactions have been reported to proceed via the latter reaction mechanism [2]. We reported previously that the thermolysis of a 1,2λ 6 -oxathietane, a pentacoordi- nated sulfurane bearing the Martin ligand [3] and a four-membered ring, gave the oxirane with retention of the relative configuration, suggesting the ligandcoupling mechanism [2].…”