Easy and efficient deracemization of all trans-1,3-diphenyl-2,4-bis-[α-hydroxybenzyl]-cyclobutane and its bisphenylsulfanyl derivative and the assignment of the absolute configuration

An effective deracemization of all trans-1,3-diphenyl-2,4-bis-[α-hydroxybenzyl]-cyclobutane 1 was achieved by the application of the (R)-(−)-O-acylmandelic acid as a resolving agent, followed by the crystallization of the diastereomeric esters. The kinetic resolution was also observed in the esterification. Racemic 1 was transformed into bisphenylsulfanyl derivative 3. Enantioselective oxidation of 3 with a VO(acac)2-chiral Schiff Base catalytic system led to a kinetic resolution, and highly enantiomerically enriched bissulfides/bissulfoxides were isolated. Assignment of the absolute configuration was made by spectroscopic methods and chemical correlation. Due to the rigid C2-symmetric framework, chiral compounds 1 and 3 have strong steric requirements and may be useful in chiral recognition.

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all trans-1,3-Diphenyl-2,4-bis-[α-(2-acetoxy-2-phenyl)acetoxy-benzyl]-cyclobutaneC50H42O8[α]D20=-86.6 (0.978, CHCl3)Source of chirality: deracemizationAbsolute configuration: (S,S)

all trans-1,3-Diphenyl-2,4-bis-[α-phenylsulfanyl-benzyl]-cyclobutaneC42H36S2[α]D20+147.6 (1.016, CHCl3)Source of chirality: kinetic resolutionAbsolute configuration: (R,R)

all trans-1,3-Diphenyl-2,4-bis-[α-phenylsulfinyl-benzyl]-cyclobutaneC42H36O2S2[α]D20+87.0 (1.924, CHCl3)Source of chirality: asymmetric inductionAbsolute configuration: (R,R,SS,SS)