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benzylmalonate. Even in this case it was not possible to remove the
References and notes
protecting group after cyclization to oxetane derivative.
As a result of these findings a different strategy was considered.
Intermediate 10 was deprotected with success by hydrogenation to
obtain triol 13 (Scheme 5).10 Treatment of this intermediate with
BuLi and tosyl chloride afforded a complex mixture, with no selec-
tive formation of poly-tosylated species besides mono-tosyl deriva-
tive. The cyclization to oxetane was accomplished by treatment of
the triol with diethyl carbonate, via formation of the corresponding
cyclic carbonate 14, followed by thermal decomposition to obtain
compound 12.12
This intermediate was then submitted to oxidation with KMnO4
to obtain carboxylic acid 15. Treating this intermediate with diph-
enylphosphorylazide (DPPA) in the presence of benzyl alcohol
afforded N-Z-protected amino-oxetane 16 in good yield. The final
deprotection under phase transfer conditions gave the free ami-
no-oxetane derivative 17. Recently the synthesis of the tert-butyl-
sulfinimine of compound 17 was described;13 the use of
organometallic reagents makes that approach alternative to the
one described in this Letter.
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In summary we developed efficient synthetic pathways for the
preparation of 3,3-disubstituted oxetane building blocks, bearing
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can in principle be applied to a large number of oxetane deriva-
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Acknowledgment
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The authors gratefully acknowledge Dr. Filippo Magaraci (Rot-
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Supplementary data
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Supplementary data (1H NMR spectra of all described com-
pounds) associated with this article can be found, in the online ver-