Sulfoxide-Carbodiimide Reactions. III.¹ Mechanism of the Oxidation Reaction

Abstract

values calculated from known bond moments and ring conformations.A dipole moment of 1.87 D. has been reported13 for tetrahydrothiophene. If one takes the CSC angle in this compound as loo", the observed moment can be considered as the vector sum of two CS bond moments of 0.935/cos 50", or 1.46 D.Bond angles and bond lengths in 1,2-dithiolane-4carboxylic acid have been determined by Foss and TjomslandZ1 based on X-ray diffraction studies. Based upon their data, the average angle between the valence bonds of each sulfur atom is 94.6" and the value of the dihedral angle between the CSS plane and the SSC plane is 26.6'. Then, by assuming the angular conformation of the 1,2-dithiolane ring in 2,3-dithiaspiro [4,5]decane to be the same as in the corresponding carboxylic acid, neglecting any small contribution of the cyclohexane ring, and taking 1.46 D. as the C-S bond moment, the calculated moment of 2,3-dithiaspiro-[4S]decane is 2.82 D., in good agreement with the observed moment of 2.85 D.The moments of the selenium-containing compounds cannot be treated so precisely because of lack of information about the C-Se-Se bond angles. However, monoselenides usually have moments only slightly smaller than monosulfides,22 and it is, therefore, not (21) 0. Foss and 0. Tjomsland, Acra Chem. Scand., 12, 1810 (1958). (22) For exainp.e, the moment of diphenyl sulfide is quoted as 1.5 D., that of diphenyl se:enide 1.4 D.: R. J. W. Le Fevre, "Dipole Moments,"Methuen and Co., Ltd., London, 1963, pp 134,135. unexpected to find that the dithiolanes and diselenolanes have similar moments or that the moment of the thiaselenenates, in the absence of a significant degree of polarization, is again similar to those of its iso-Turning now to the carboxylic acids, 1,2-dithiolane-4carboxylic acid (I) can be treated as containing a planar ring with a moment of 2.85 D. The contribution of the carboxyl group in I is taken from the observed moment of cyclopentanecarboxylic acid (1.70 D.) and the angle of the C-COOH bond to the plane of the ring is assumed to be one-half the normal tetrahedral angle of 110". The angle of the carboxyl moment to the C-COOH bond is taken as 74°.23Hydrogen bonding of the carboxylic hydrogen to the disulfide bond would restrict rotation of the carboxyl group and result in a molecule with conformation Ia, having a calculated dipole moment of 1.4 D. Conversely, conformation Ib, resulting from interaction of the S-S bond with the carbonyl oxygen, would produce a moment of 4.1 D. The moments observed for the free acids as well as for the methyl ester of 1,2-dithiolane-4-carboxylic acid are in surprisingly good agreement with the moment calculated assuming unrestricted rotation of the carboxyl group, 3.1 D. This further substantiates the contention that little, if any, interaction occurs between the carboxyl group and the disulfide bond. logs.Abstract: The mechanism of the oxidation reaction resulting from treatment of an alcohol with dimethyl sulfoxide and dicyclohexylcarbodiimide in the presence of a proton source has be...

Steroids and Steroidases: Iii. Dicyclohexylcarbodiimide–dimethyl Sulfoxide Oxidations of Alcohols and Thiols

“…In no case \vas a disulfide product detected, and the starting nlercaptans were recovered unchanged. These results, together \\.it11 those of Wallace and his co-wor1;crs (IS, 19), ~1 1 0 sho\ved that oxidation of thiols by D l I S O alone proceeded via ionic intermediates \\-ith the formation of dimethyl s~l f i d e ,~ suggest that the initial stages of thiol oxidation by DCC-D l I S O are sinlilar to those established for alcohols (12), as irldicnted in Diagra~ii 2.…”

“…T h e results of the studies carried out on the mechanisn~ by u~hich the hlloffatt reagent effects oxidation (7,9,12) are in accord \\-it11 the forination of the intcrmediate X. In a n attempt t o obtain further evidence for its existence, various mixtures of DCC, P'TFA, and DMSO were examined by infrared and protoil magnetic resonance spectroscopy.…”

“…T h e data curreiltly available (7)(8)(9)(10)(11)(12) indicate t h a t the metl~yltl~iomethoxy ccinpounds are fornled by Puillmerer rearrangement (13) of intermediates such as VI. Formation of a inethyltl~ioinethoxy derivative froin this type of interinediate can occur either by rearrangement through a n ion pair such as VII (path A, Diagranl 1) or intrainolecularly as sho\vn in path 13, Diagram Froin the data of Johnsoil (14) and Parham (15) and their collaborators and by analogy wit11 the cleavage-recombination inechanisms proposed for the Stevens and Wittig reactions (lG), to which the Puminerer rearranyeinent seeins closely related, it urould appear that path A is the inore probable.…”

Acylation Mechanisms of DMSO/[D6]DMSO with Di‐tert‐butylketene and Its Congeners

“…This change‐over of the rate‐limiting step establishes a novel mechanistic variant of the Pummerer acylation in which the overall reaction rates of DMSO and [D 6 ]DMSO (but not the faster C–H/C–D bond fissions) are almost equally slow. The large amount of acid 3 observed in situ is informative: If thesulfonium ylide t Bu 2 CHCO 2 –S + (CD 3 )CD 2 – had been formed13,20 from [D 6 ] 6 , it would be expected to be rapidly protonated by 3 to give t Bu 2 CHCO 2 –S + (CD 3 )CHD 2 and finally [D 4 ] 4 or a less highly deuteriated product; but this was never detected. Consequently, the sulfonium ylide is formed in step 2 either irreversibly21 (faster decay to afford [D 5 ] 8 ) or not at all (faster E2 elimination of [D 6 ] 6 ).…”

Esterification of Polysaccharides

“…In the case of esterification of polysaccharides in DMSO in the presence of these reagents, oxidation of hydroxyl functions may occur due to a Moffatt-type reaction (Fig. 5.22, [211]). …”