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DOI: 10.1055/s-2004-822914
Base-Dependent Regio- and Diastereoselective Alkylation of Chiral Perhydro 1,3,2-Oxazabenzophosphorinane-2-oxides Derived from (-)-8-Benzylamino Menthol
Publikationsverlauf
Publikationsdatum:
28. April 2004 (online)
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Abstract
The regioselectivity in the alkylation of chiral perhydro 1,3,2-benzoxazaphosphorinane-2-oxides is dependent on the base used for deprotonation. The ethyl oxazaphosphorinanes are benzylated at the nitrogen substituent after deprotonation with n-BuLi, but α to the phosphorous atom by deprotonation with LDA. On the contrary, the benzyl oxazaphosphorinane is alkylated α to the phosphorous atom after deprotonation with both, n-BuLi or LDA.
Key words
alkylation - alkyl phosphonates - asymmetric synthesis - diastereoselective reactions - 2-oxo-1,3,2-oxazaphosphorinanes
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References
CCDC contain supplementary crystallographic data for compounds 1 (CCDC 233645), 2 (CCDC 233647), 4 (CCDC 233644), and 8 (CCDC 233646), respectively. These data can be obtained free of charge at www.ccdc.cam.ac.uk/conts/retreiving.html or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB12 1EZ, UK; fax: (internat.) +44(1223)336033; e-mail: deposit@ccdc.cam.ac.uk.
14Typical Experimental Procedure: To a cooled (-78 °C) solution of the corresponding 1,3,2-oxazaphosphorinane (0.9 mmol) in dry THF (20 mL) under argon atmosphere was added the base (1.8 mmol), and the mixture was stirred for 30 min. Then, benzyl bromide (1.8 mmol) was added and the stirring was continued until the reaction was finished (TLC). The reaction was quenched with H2O (9 mL) and stirred until the mixture was reached r.t. THF was removed under reduced pressure and the aqueous mixture extracted with CH2Cl2 (3 × 25 mL). The combined organic layers were dried (MgSO4), filtered and concentrated. The residue was purified by flash chromatography on silica gel and hexane-EtOAc (1:2) as eluent.