Synthesis of Enantiomerically Pure Thiocrown Ethers Derived from 1,1'-Binaphthalene-2,2'-diol.

Abstract

Synthetic methodology is given for the preparation of two different types of thiocrown ethers from optically pure 1,1'-binaphthalene-2,2'-diol (10). The conceptually simplest approach starts from optically pure 10 itself, which is alkylated (4 equiv of K(2)CO(3) in DMF at 110 degrees C) with 2-chloroethanol followed by mesylation to provide 2,2'-bis(2-(mesyloxy)ethoxy)-1,1'-binaphthyl (14). When allowed to react with ethane-1,2-dithiol, propane-1,3-dithiol, 1,4,7-trithiaheptane, 1,4,8,11-tetrathiaundecane, 2,2-dimethylpropane-1,3-dithiol, 2-(mercaptomethyl)-1-propene-3-thiol, and 1,2-benzenedithiol in the presence of Cs(2)CO(3) in DMF at 60 degrees C the corresponding thiocrown ethers 22-25, 28, 30, and 32 are formed in 30-54% yields. Test reactions were carried out to establish that no racemization occurs during alkylation under these conditions. Reaction of optically pure 10 with tetrahydropyranyl (THP)-protected 3-chloropropanol under similar conditions for the preparation of 14 proceeded more sluggishly but cleanly. Removal of the THP protecting groups afforded 2,2'-bis(3-bromopropoxy)-1,1'-binaphthyl (20), which on reaction with propane-1,3-dithiol, 1,5,9-trithianonane, 2,2-dimethylpropane-1,3-dithiol, 2-(mercaptomethyl)-1-propene-3-thiol, and 1,2-bis(mercaptomethyl)benzene provided the respective thiocrown ethers 26, 27, 29, 31, and 33 in 24-68% yields. Another class of thiocrown ethers was prepared from optically active 10, which was converted via ortho-lithiation to 3,3'-bis(bromomethyl)-2,2'-dimethoxy-1,1'-binaphthyl (39) by means of methylation (K(2)CO(3)/CH(3)I), ortho-lithiation followed by formylation (n-C(4)H(9)Li/N,N,N',N'-tetramethylethylenediamine (TMEDA)/ether followed by DMF and H(2)O workup) followed by reduction (NaBH(4)) followed by bromination (PBr(3) in C(5)H(5)N). Reaction (Cs(2)CO(3) in DMF at 60 degrees C) with 1,4,7-trithiaheptane, 1,4,8-trithiaoctane, 1,4,7,10-tetrathiadecane, 1,4,8,11-tetrathiaundecane, and 1,5,10,14-tetrathiatetradecane afforded the corresponding thiocrown ethers 40-44 in 40-75% yields. Despite repeated attempts using a wide range of reagents, demethylation of the methoxy ether functionalities failed. Attempts to prepare the free phenol derivatives of the latter type of crown ethers by oxidative coupling of two naphthol units failed.