Oxaziridines 2-sulfonyl

Davis and coworkers40 have developed use of diastereomerically pure 2-sulfonyl and 2-sulfamyloxaziridines for asymmetric oxidation of sulfides into sulfoxides (equation 7). The best results (using the sulfamyloxaziridines) range from 38 to 68% enantiomeric purity of the resultant sulfoxides. The structural diversity of such substituted oxaziridines, their... 

Davis et al.111 developed another method for reagent-controlled asymmetric oxidation of enolates to a-hydroxy carbonyl compounds using (+)-camphor-sulfonyl oxaziridine (147) as the oxidant. This method afforded synthetically useful ee (60-95%) for most carbonyl compounds such as acyclic keto esters, amides, and a-oxo ester enolates (Table 4-20). 

Thioxo-1,2,4-dithiazolidines can be obtained from thioxo-l,2,4-thiadiazolidines by Dimroth rearrangement (Scheme 47) or reversibly by addition and elimination of acetone (Scheme 22). 1,2,4-Dithiazole type products are also obtained from thiocarbonyl isothiocyanates (154) by reaction with CI2 <84CHEC-I(6)897>, PhMgBr, Sj, or CS2. Other routes include reactions of carbonyl isothiocyanates and thiocarbonyl isocyanates with P4S10 or Sg <84Chec-I(6)897> and sulfonyl isocyanates with dialkyl thioketenes. Phenylisothiocyanate heated with N,C-disubstituted oxaziridines affords 3,5-diimino-l,2,4-dithiazolidines (226, 227). Other miscellaneous syntheses of 1,2,4-dithiazoline derivatives include cyclization of A7-thioacyl hexafluoroacetonimine to 5,5-bis(trifluoromethyl)-... 

Epoxidation of both aldimines and ketimines is possible. Most oxaziridines formed are stable compounds, especially aldimines containing aromatic substituents, and 2-sulfonyl-and 2-sulfamyl oxaziridines5. Generally, /V-sulfonyloxaziridines are isolated as stable crystalline solids. Certain compounds are widely used in synthetic organic chemistry as oxygen-transfer reagents (15-17). 

Biphasic buffered oxidation of sulfonylimines usually suffice for stereoselective synthesis of fraws-sulfonyl substituted oxaziridines in excellent yields (equation 41)203. 

In the N-sulfonyl imine-catalyzed sulfoxidation, aqueous hydrogen peroxide serves as the final oxidizing agent, which is clearly of practical advantage. In principle it can be assumed that either an oxaziridine (F, Scheme 10.17) or a hydroper-oxy hemiaminal (H, Scheme 10.17) can result as the active species from the reaction of the N-sulfonyl imine E with hydrogen peroxide (Scheme 10.17). For imine 79 the idea of an intermediate oxaziridine is supported by the experimental finding that oxidation by the isolated oxaziridine and in the catalytic reaction (using 79 and... 

Biphasic basic oxidation using technical grade (50-60%) 3-chloroperbenzoic acid affords this oxaziridine in - 4 hr In a 2-L, three-necked, Morton-flask equipped with a mechanical stirrer was placed 22.6 g (0.083 mol) of crude (+)-[(7,7-dimethoxycamphoryl)sulfonyl]imine, 42.6 g (0.13 mol) of 3-chloroperoxybenzoic acid (50-60%) in 450 mL of methylene chloride, and 450 mL of saturated potassium carbonate solution. The reaction mixture was stirred vigorously until the oxidation was complete as indicated by TLC (Note 27) at which time 500 mL of water was added, the organic layer was separated and the aqueous layer was extracted with methylene chloride (2 x 500 mL). The combined organic extracts were washed with saturated sodium sulfite (300 mL) and water (300 mL), and dried over anhydrous magnesium sulfate. 

Oxidation of (+)-[(7,7-dimethoxycamphoryl)sulfonyl]imine (96%) and (+)-[(7,7-dichlorocamphoryl)sulfonyl]imine (98%)10 with 3-chloroperbenzoic acid has been reported. The procedure described here uses less hazardous and less expensive peracetic acid with the aid of Aliquat 336.10 However, this system requires 40 hr vs. 4 hr using 3-chloroperbenzoic acid for oxidation of (+)-[(7,7-dimethoxy-camphoryl)sulfonyl]imine to the oxaziridine. 

S,8aR )-[(8,8-Dimethoxycamphoryl)sulfonyl]oxaziridine 4H-4a,7-Methanooxazirino[3,2-i](2,1]benzisothiazole, tetrahydro-8,8-dimethoxy-9,9-dimethyl-,... 

R,8aR )-[(8,8-DIMETHOXY-CAMPHORYL)SULFONYL]OXAZIRIDINE AND (+)-(2R,8aR )-[(8l8-DICHLORO-CAMPHORYL)SULFONYL]-OXAZIRIDINE... 

Dihydro-2-hydroxy-2-methyl-l(2//)-naphthalenone (7), a model for many natural products, is obtained in >95% ee via oxidation of the sodium enolate of 3,4-dihydro-2-methyl-1 (2f/)-naphthalenone (5) with ( + )-[(8,8-dichlorocamphoi)sulfonyl]oxaziridine (6)88. This material was obtained in less than 16% ee using (j-)-(camphorsulfonyl)oxaziridine 26. 

Tabic 9. Enantioselective x-Oxygcnation of Prostereogcnic Enolates with Enantiomerically Pure rV-Sulfonyl-oxaziridines ... 

By far the most widely used synthetic application of the oxaziridines is oxidation. The aptotic A -sulfonyl- and peroxaziridines transfer oxygen at rates comparable to peracids via a mechanism where the nucleophilic species attacks the electrophilic oxaziridine oxygen atom in an SN2-type fashion <1996CHEC-II(1A)365>. 

As discussed previously, treatment of thiolates generated from thiols and MeLi with sterically hindered A -sulfonyl-oxaziridine 116 gave the corresponding sulfenate intermediates which were alkylated to afford sulfoxides 118 (Equation 4) <1997JOC8626, 1999PS(153)381, 2004JOC6916>. Oxidation of thiolates generated from aryl thiols... 

Preparative Methods the enantiopure (+)- and (—)-(cam-phorylsulfonyl)oxaziridines (1) and [(8,8-dichlorocam-phor)sulfonyl]oxaziridines (2) are commercially available. They can also be prepared on a large scale via the oxidation of corresponding camphorsulfonimines with buffered Potassium Monoperoxysulfate (Oxone) or buffered peracetic acid. Since oxidation takes place from the endo face of the C=N double bond, only a single oxaziridine isomer is obtained. The precursor camphorsulfonimines can be prepared in 3 steps (>80% yield) from inexpensive (+)- and —yiO-Camphorsulfonic Acids. A variety of (camphorylsul-fonyl)oxaziridine derivatives such as (2)-(4) are also readily available via the functionalization of the camphorsulfonimines followed by oxidation. " ... 

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