New chiral amino acid-derived α-acyloxynitroso reagents for asymmetric nitroso Diels–Alder reactions

The preparation of new chiral α-acyloxynitroso derivatives 4a–e as chiral dienophiles for the nitroso Diels–Alder reaction is reported. These compounds are obtained from amino acid-derived iodobenzene dicarboxylates and ketoximes, and are stable and easy-to-handle reagents. Initial studies for their nitroso Diels–Alder reactions with cyclohexadiene are also reported.

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(1′-Nitroso-1′-cyclohexyl)-2-phthalimido propionateC17H18N2O5Ee >93% (HPLC)[α]D = +27.9 (c 0.66, CHCl3)Source of chirality: l-alanineAbsolute configuration: (S)

(1′-Nitroso-1′-cyclohexyl)-3-methyl-2-phthalimido butyrateC19H22N2O5Ee >96% (HPLC)[α]D = +86.1 (c 0.55, CH2Cl2)Source of chirality: l-valineAbsolute configuration: (S)

(1′-Nitroso-1′-cyclohexyl)-4-methyl-2-phthalimido pentanoateC20H24N2O5Ee >96% (HPLC)[α]D = +32.4 (c 0.44, CH2Cl2)Source of chirality: l-leucineAbsolute configuration: (S)

(1′-Nitroso-1′-cyclohexyl)-3-phenyl-2-phthalimido propionateC23H22N2O5Ee >94% (HPLC)[α]D = −76.5 (c 0.44, CH2Cl2)Source of chirality: l-phenylalanineAbsolute configuration: (S)

(1′-Nitroso-1′-cyclohexyl)-1-tertbutyloxycarbonyl-1-pyrrolidine -2-carboxylateC16H26N2O5[α]D = −84.0 (c 0.61, CH2Cl2)Source of chirality: l-prolineAbsolute configuration: (S)