Chiral linker 5: scope and limitations of arylsubstituted m-hydrobenzoins as solid supported open chain chiral auxiliaries for diastereoselective syntheses

The applicability of five aryl substituted m-hydrobenzoin ethers already tested in the L-Selectride® mediated stereoselective reduction of phenylglyoxylates as open chain chiral auxiliaries was further investigated via the α-alkylation of propionates, the addition of n-BuZnCl to phenylglyoxylates and the Diels–Alder reaction of acrylates with cyclopentadiene as model reactions. As up to 90% de could be achieved in the solution phase, two optimized auxiliary structures were immobilized on commercially available Wang-resin and applied as a reusable solid supported chiral auxiliaries in the same type of reactions.

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Propanoic acid (1R,2S)-1,2-bis(2-methoxyphenyl)-2-(2-methoxyethoxy)ethyl esterC22H28O6Ee = >98%[α]D20=+17.8 (c 1.00, CH2Cl2)Source of chirality: [(2R)-(2a, 3aa, 4b, 7b, 7a)] octahydro-7,8,8-trimethyl-4,7-methanobenzafuran-2-olAbsolute configuration: (1R,2S)

Propenoic acid (1R,2S)-2-(2-methoxyethoxy)-1,2-diphenylethyl esterC20H22O4Ee = >98%[α]D20=+27.2 (c 1.00, CH2Cl2)Source of chirality: [(2R)-(2a, 3aa, 4b, 7b, 7a)] octahydro-7,8,8-trimethyl-4,7-methanobenzafuran-2-olAbsolute configuration: (1R,2S)

Propenoic acid (1R,2S)-2-(2-methoxyethoxy)-1,2-bis(2-methoxyphenyl)ethyl esterC22H26O6Ee = >98%[α]D20=+40.7 (c 0.95, CH2Cl2)Source of chirality: [(2R)-(2a, 3aa, 4b, 7b, 7a)] octahydro-7,8,8-trimethyl-4,7-methanobenzafuran-2-olAbsolute configuration: (1R,2S)

Propenoic acid (1R,2S)-1,2-bis(2-methoxyphenyl)-2-(2-methylpropoxy)ethyl esterC23H28O5Ee = >98%[α]D20=+58.3 (c 1.17, CH2Cl2)Source of chirality: [(2R)-(2a, 3aa, 4b, 7b, 7a)] octahydro-7,8,8-trimethyl-4,7-methanobenzafuran-2-olAbsolute configuration: (1R,2S)

Propanoic acid (1R,2S)-1,2-bis(2-methoxyphenyl)-2-(2-methylpropoxy)ethyl esterC23H30O5Ee = >98%[α]D20=+38.9 (c 0.70, CH2Cl2)Source of chirality: [(2R)-(2a, 3aa, 4b, 7b, 7a)] octahydro-7,8,8-trimethyl-4,7-methanobenzafuran-2-olAbsolute configuration: (1R,2S)

Propanoic acid (1R,2S)-1,2-bis(2-methylphenyl)-2-(2-methylpropoxy)ethyl esterC23H30O3Ee = >98%[α]D20=+53.3 (c 1.07, CH2Cl2)Source of chirality: [(2R)-(2a, 3aa, 4b, 7b, 7a)] octahydro-7,8,8-trimethyl-4,7-methanobenzafuran-2-olAbsolute configuration: (1R,2S)

Propanoic acid (1R,2S)-1,2-bis(4-methoxyphenyl)-2-(2-methylpropoxy)ethyl esterC23H30O5Ee = >98%[α]D20=+14.4 (c 0.65, CH2Cl2)Source of chirality: [(2R)-(2a, 3aa, 4b, 7b, 7a)] octahydro-7,8,8-trimethyl-4,7-methanobenzafuran-2-olAbsolute configuration: (1R,2S)

Propanoic acid (1R,2S)-2-(2-methylpropoxy)-1,2-bis(2-trifluormethylphenyl)ethyl esterC23H24F6O3Ee = >98%[α]D20=+13.9 (c 1.10, CH2Cl2)Source of chirality: [(2R)-(2a, 3aa, 4b, 7b, 7a)] octahydro-7,8,8-trimethyl-4,7-methanobenzafuran-2-olAbsolute configuration: (1R,2S)