A compound of the formula: or a salt, or tautomer thereof, wherein R 3 is hydrogen; halogen; cyclic or acyclic, substituted or unsubstituted, branched or unbranched aliphatic; cyclic or acyclic, substituted or unsubstituted, branched or unbranched heteroaliphatic; substituted or unsubstituted acyl; substituted or unsubstituted aryl; substituted or unsubstituted heteroaryl; -OR C; -C(=O)R C; -CO 2 R C; -CN; -SCN; -SR C; -SOR C; -SO 2 R C; -NO 2;-N(R C) 2; -NHC R C; or -C(R C) 3; wherein each occurrence of R C is independently hydrogen, a protecting group, aliphatic, heteroaliphatic, acyl; aryl; heteroaryl; alkoxy; aryloxy; alkylthio; arylthio; amino, alkylamino, dialkylamino, heteroaryloxy; or heteroarylthio; R 4 is hydrogen; halogen; cyclic or acyclic, substituted or unsubstituted, branched or unbranched aliphatic; cyclic or acyclic, substituted or unsubstituted, branched or unbranched heteroaliphatic; substituted or unsubstituted acyl; substituted or unsubstituted aryl; substituted or unsubstituted heteroaryl; -OR D; -C(=O)R D; -CO 2 R D; -CN; -SCN; -SR D; -SOR D; -SO 2 R D; -NO 2;-N(R D) 2; -NHC R D; or -C(R D) 3; wherein each occurrence of R D is independently hydrogen, a protecting group, aliphatic, heteroaliphatic, acyl; aryl; heteroaryl; alkoxy; aryloxy; alkylthio; arylthio; amino, alkylamino, dialkylamino, heteroaryloxy; or heteroarylthio; R 5 is hydrogen; halogen; cyclic or acyclic, substituted or unsubstituted, branched or unbranched aliphatic; cyclic or acyclic, substituted or unsubstituted, branched or unbranched heteroaliphatic; substituted or unsubstituted acyl; substituted or unsubstituted aryl; substituted or unsubstituted heteroaryl; -OR E; -CN; -SCN; -SR E; or -N(R E) 2; wherein each occurrence of R E is independently hydrogen, a protecting group, aliphatic, heteroaliphatic, acyl; aryl; heteroaryl; alkoxy; aryloxy; alkylthio; arylthio; amino, alkylamino, dialkylamino, heteroaryloxy; or heteroarylthio; R 6 is hydrogen, halogen, substituted or unsubstituted aliphatic, substituted or unsubstituted heteroaliphatic, substituted or unsubstituted alkoxy, -OH, -CN, -SCN, -SH, alkylthio, arylthio, -NO 2, amino, alkyl amino, dialkyl amino, or -SAr, wherein Ar is substituted or unsubstituted aryl, or substituted or unsubstituted heteroaryl; and each occurrence of P' is independently hydrogen or a protecting group. wherein R 3 is hydrogen; halogen; cyclic or acyclic, substituted or unsubstituted, branched or unbranched aliphatic; cyclic or acyclic, substituted or unsubstituted, branched or unbranched heteroaliphatic; substituted or unsubstituted acyl; substituted or unsubstituted aryl; substituted or unsubstituted heteroaryl; -OR C; -C(=O)R C; -CO 2 R C; -CN; -SCN; -SR C; -SOR C; -SO 2 R C; -NO 2;-N(R C) 2; -NHC R C; or -C(R C) 3; wherein each occurrence of R C is independently hydrogen, a protecting group, aliphatic, heteroaliphatic, acyl; aryl; heteroaryl; alkoxy; aryloxy; alkylthio; arylthio; amino, alkylamino, dialkylamino, heteroaryloxy; or heteroarylthio; R 4 is hydrogen; halogen; cyclic or acyclic, substituted or unsubstituted, branched or unbranched aliphatic; cyclic or acyclic, substituted or unsubstituted, branched or unbranched heteroaliphatic; substituted or unsubstituted acyl; substituted or unsubstituted aryl; substituted or unsubstituted heteroaryl; -OR D; -C(=O)R D; -CO 2 R D; -CN; -SCN; -SR D; -SOR D; -SO 2 R D; -NO 2;-N(R D) 2; -NHC R D; or -C(R D) 3; wherein each occurrence of R D is independently hydrogen, a protecting group, aliphatic, heteroaliphatic, acyl; aryl; heteroaryl; alkoxy; aryloxy; alkylthio; arylthio; amino, alkylamino, dialkylamino, heteroaryloxy; or heteroarylthio; R 5 is hydrogen; halogen; cyclic or acyclic, substituted or unsubstituted, branched or unbranched aliphatic; cyclic or acyclic, substituted or unsubstituted, branched or unbranched heteroaliphatic; substituted or unsubstituted acyl; substituted or unsubstituted aryl; substituted or unsubstituted heteroaryl; -OR E; -CN; -SCN; -SR E; or -N(R E) 2; wherein each occurrence of R E is independently hydrogen, a protecting group, aliphatic, heteroaliphatic, acyl; aryl; heteroaryl; alkoxy; aryloxy; alkylthio; arylthio; amino, alkylamino, dialkylamino, heteroaryloxy; or heteroarylthio; R 6 is hydrogen, halogen, substituted or unsubstituted aliphatic, substituted or unsubstituted heteroaliphatic, substituted or unsubstituted alkoxy, -OH, -CN, -SCN, -SH, alkylthio, arylthio, -NO 2, amino, alkyl amino, dialkyl amino, or -SAr, wherein Ar is substituted or unsubstituted aryl, or substituted or unsubstituted heteroaryl; and each occurrence of P' is independently hydrogen or a protecting group.