Davy reagents

Cyclopropylpropiolic acid ethyl ester, 66, 177 Davis reagent, 66, 203... 

Davy reagents 32,38 decarboxylation 64,67 Dehydrogenation of ketones 55 Dehydrohalogenation 57 Deracemization 68 Desulfurization 75 of dithioacetals 78,100 of dithioesters 69... 

An anomalous reaction of 2-benzenesulfonyl-3-aryloxaziridines (Davis reagents) with indoles has been reported.48 hi this it appears that a re-bond in the indole acts nucleophilically to attack the O of the oxaziridine ring and thereby cleave the O—N bond. 

Acetalization of thiochroman-3-one gives a 1 1 diastereomeric mixture and subsequent oxidation with Davis reagent, W-(phenylsulfonyl)(3,3-dichlorocamphoryl)oxaziridine, yielded the sulfoxides each with a 4 1 enantioselectivity. Chiral chromatographic separation of the diastereomers preceded isolation of the major enantiomers. (3-Elimination and isomerization of the double bond then produced the individual thiochromene 1-oxide diastereomers. The generation of an a-sulfinyl carbanion effects the cleavage of one of the acetal C-O bonds with the protected diol released in a final ozonolysis step. The stereochemical results indicate that it is the C-O bond syn to the sulfoxide function that is cleaved (Scheme 63) <1996TA29>. 

Hydroxylation of amide and lactam enolates using Davis reagents (Section 2.3.2.1.2.iii) occurs readily at low temperature. The process can be highly stereoselective and is viaUe for oxidation of both sec-... 

Phenylsu onyl) 3 phenytoxazmdine (Davis reagent) 90 Phosphmimine 247,269 Phosphine tiiphenyt 222 359 PhosphSe methyl 8,359 Phosphorus red 163... 

While the majority of examples of substrate control deal with cyclic sterocontrol, there are a few examples where diasteroselectivity is induced in an acylic system.27 A notable example of this was demonstrated during the synthesis of a fragment of tubulysin, by Wipf and co-workers.28 Utilizing a Davis reagent in their synthesis of an a-hydroxy-y-amino acid, the enolate of the y-amino acid derivative 42 was reacted with 1 to form the a-hydroxy derivative 43 as a single diastereomer in good yield. The stereoselective reaction has precedence in literature and likely involves a highly chelated dianionic species.29... 

Further examples of acyclic stereocontrol in related amino acid systems make use of chiral and nonracemic oxaziridine reagents to induce high levels of stereocontrol. In 1992, Davis and coworkers synthesized the methyl ester of the Taxol C13 side chain using this method.30 Following enolization, the dianion of 44 was reacted with the Davis reagent 5 to yield the a-hydroxy (5-amino acid 45 in 49% yield. While the yield was marginal in this particular example, the 86 14 ratio of stereoisomers produced is impressive in this acyclic system. 

Substrate directed hydroxylation with Davis reagents has also found utility in the synthesis of architecturally complex natural products. 4 For example, efforts for the synthesis of (+)-spongistatin 1 by Smith and co-workers relied on hydroxylation of the enolate of 54 with Davis reagent 7, which was followed by epimerization of the Cs to produce 55 in high yield.45... 

Several examples exist in the literature in which cyclic ketone enolates are enantioselectively hydroxylated by chiral, nonracemic Davis oxaziridine reagents. In contrast to their acyclic counterpart, the enolate geometry is fixed in cyclic systems. During the preparation of enantiomerically pure (-)-blebbistatin, the enolate of the quinolone 61 was reacted with the Davis reagent 5 to afford the optically enriched 62 with 82% yield and 86% ee.54 The related reagent 6 was used in the synthesis of (-t-)-o-trimethylbrazilin, which was... 

Sulfenimines undergo asymmetric oxidations to form sulfinimines via a reaction with Davis reagents. The sulfenimine 77 was oxidized by 9 to yield the sulfmimine 78 in 82% yield and 97% ee. Yields and enantiomeric excess varied based on the oxaziridine reagent used.64... 

Reagents and conditions i) Davies reagent i) trichloroacetic anhydride iii) DMAP, toluene iv) aciytoyl chioride, NEta, CHaCis v) Ri-NHj DMSO vi) R2-N=C=0 vS) HCI, toluene, 95°C viii) TFA ix) BrCN, TFA. CHCla aO.345... 

---