105857-52-1Relevant articles and documents
Enantioselective Functionalization of Prochiral Diols via Chiral Spiroketals: Preparation of Optically Pure 2-Substituted 1,3-Propanediol Derivatives and Asymmetric Synthesis of Chroman Ring and Side Chain of α-Tocopherol
Harada, Toshiro,Hayashiya, Toshio,Wada, Isao,Iwa-ake, Naoko,Oku, Akira
, p. 527 - 532 (2007/10/02)
The enantioselective functionalization of a prochiral hydroxyl group in 2-substituted 1,3-propanediols (HOCH2CR1R2CH2OH) is presented.The reaction of the bis(trimethylsilyl) derivative of the diol with l-menthone in the presence of trimethylsilyl trifluoromethanesulfonate selectively gave one of the diastereomers of the spiroketal in which the larger substituent (R1) occupies an equatorial position.The equatorial spiroketal was treated with acetophenone enol trimethylsilyl ether in the presence of titanium tetrachloride to give the ring-cleavage product which was produced by the selective cleavage of the equatorial C-O bond.After a proper functionalization of the hydroxyl group, the chiral auxiliary was removed under basic conditions to give the optically pure (>95percent ee) derivatives 5. The stereoselective preparation of the axial spiroketal (R1 = H, R2 = Me) and its ring-cleavage are also described.The potentiality of the present method is demonstrated in an asymmetric synthesis of (2R,6R)-2,6,10-trimethylundecanol and (S)-6-benzyloxy-3,4-dihydro-2,5,7,8-tetramethyl-2H-benzopyran-2-methanol which are key intermediates in the total synthesis of naturally occuring (2R,4'R,8'R)-α-tocopherol.