Alcohols, allylic with aziridines esters

The stereochemistry of the first step was ascertained by an X-ray analysis [8] of an isolated oxazaphospholidine 3 (R = Ph). The overall sequence from oxi-rane to aziridine takes place with an excellent retention of chiral integrity. As the stereochemistry of the oxirane esters is determined by the chiral inductor during the Sharpless epoxidation, both enantiomers of aziridine esters can be readily obtained by choosing the desired antipodal tartrate inductor during the epoxidation reaction. It is relevant to note that the required starting allylic alcohols are conveniently prepared by chain elongation of propargyl alcohol as a C3 synthon followed by an appropriate reduction of the triple bond, e. g., with lithium aluminum hydride [6b]. 

All types of electrophiles have been used with 2-lithio-l,3-dithiane derivatives, including alkyl halides, sulfonates, sulfates, allylic alcohols, arene-metal complexes, epoxides, aziridines, carbonyl compounds, imines, Michael-acceptors, carbon dioxide, acyl chlorides, esters and lactones, amides, nitriles, isocyanates, disulfides and chlorotrialkylsilanes or stannanes. The final deprotection of the dithioacetal moiety can be carried out by means of different types of reagents in order to regenerate the carbonyl group by heavy metal coordination, alkylation and oxidation184 or it can be reduced to a methylene group with Raney-nickel, sodium or LiAIII4. 

Kawahata and Goodman utilized a chiral aziridine 166 as a simple precursor for the synthesis of / -aminoacids <1999TL2271>. The chiral aziridine is prepared in five steps from the corresponding allylic alcohol via a Sharpless asymmetric epoxidation. A one-electron reduction of aziridine 166 with SmG provided the ring-opened aziridine. Protection of the resulting amine as the BOC-derivative provided a 1.6 1 mixture of the BOC-amino ester diaster-eomers 167a and 167b in 66% yield (Equation 50). 

Carbon-Oxygen Bond Formation. CAN is an efficient reagent for the conversion of epoxides into /3-nitrato alcohols. 1,2-cA-Diols can be prepared from alkenes by reaction with CAN/I2 followed by hydrolysis with KOH. Of particular interest is the high-yield synthesis of various a-hydroxy ketones and a-amino ketones from oxiranes and aziridines, respectively. The reactions are operated under mild conditions with the use of NBS and a catalytic amount of CAN as the reagents (eq 25). In another case, N-(silylmethyl)amides can be converted to A-(methoxymethyl)amides by CAN in methanol (eq 26). This chemistry has found application in the removal of electroauxiliaries from peptide substrates. Other CAN-mediated C-0 bondforming reactions include the oxidative rearrangement of aryl cyclobutanes and oxetanes, the conversion of allylic and tertiary benzylic alcohols into their corresponding ethers, and the alkoxylation of cephem sulfoxides at the position a to the ester moiety. 

Sulfur Chemistry - Two facile methods of the heretofore difficult sulfoxide to sulfide reduction have been accomplished with dilsobutyl aluminum hydride and dichloroborane in THF at 0 . With the latter reagent, ketones, esters, and amides remain unaffected. A review on sulfoximes and derivatives as synthetic reagents presents some new methods for the preparation of various oxiranes, aziridines, alcohols, cyclopropanes, and alkenesAllylic sulfoxide anions have proven useful for the synthesis of ally lie alcohols, including trisubstltuted olefinic allylic alcohols. Transesterification between a dialkylacylphosphonate and a sulfonic acid yields sulfonate esters. The oxidation of aliphatic mercaptans to sul-finio acids with the use of m-chloroperbenzoic acid is especially useful in that the excess perbenzolc acid is removed by precipitation at -80. ... 

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