1,2-Cyclopentanediol chirality

Triphenylbismuth(V) diacetate acts as O-phenylating agent of alcohols. The reaction of ci s-l, 2-cyclopentanediol catalyzed by a Cu(II) acetate-chiral pyridinyloxazoline combined system gives the mono-phenylation product in up to 50% ee (Scheme 127) (307). 

In the presence or absence of a copper catalyst, O-arylation of alcohols and phenols by Ph3Bi(OAc)2 proceeds to give the corresponding aryl ethers.196-198 The monophenylation of m-l,2-cyclopentanediol with Ph3Bi(OAc)2 in the presence of a Cu(n) complex bearing a chiral triamine or diamine ligand affords an a-hydroxy phenyl ether with moderate enantiomeric excesses up to 38% (Equation (127)).199 The copper-catalyzed O-arylation has been success-fully applied to the synthesis of immunosuppressive macrolides. 

Figure 58 Partial 13C NMR spectra for (R,R)-trans-1,2- diaminocyclohexane-( )-irani-l, 2-cyclopentanediol and (R)-l,l -bi-2-naphthol adducts. Left (a) (R,R)-trans-1, 2-diaminocy-clohexane (b) inms-( )cyclopentanediol (c) 1 1 adduct between (R,R)-trans-1, 2-diamino-cyclohexane and tranx-( )-cyclopentanediol (d) 0.5 1 adduct between (R,R)-trans-1, 2-diaminocyclohexane and Znms-(+/-)-cyclopentanediol. Right (a) (R,R)-trans-1, 2-diami-nocyclohexane (b) 1 1 adduct between (i )-l,l -bi-2-naphthol and trans-( )-1, 2-diaminocyclohexane (c) 1 1 adduct between R,R)-trans-1, 2-diaminocyclohexane and (2 )-1,1 -bi-2-naphthol (e.e. 35%) showing molecular recognition and chiral discrimination of the diastereomeric supraminols (d) 1 1 adduct between (R)-l,l -bi-2-naphthol and (R,R)-trans-1, 2-diaminocyclohexane [60],...

If we examine models of c/a- and /ra/75-K2-cyclopentanediol more closely, we find that each compound contains two chiral centers. We know (Sec. 4.18) that compounds containing more than one chiral center are often -but not always —chiral. Are these glycols chiral As always, to test for possible chirality, we construct a model of the molecule and a model of its mirror image, and see if the two are superimposable. When we do this for the trans-g yco, we find that the models... 

Next let us look at c/5-l,2-cyclopentanediol. This, too, contains two chiral centers is it also chiral This time we find that a model of the molecule and a model of its mirror image are superimposable. In spite of its chiral centers, c/5-1,-2-... 

Cyclopentanediol also has two chiral centers therefore, the 2" rule predicts a maximum of 2 = 4 stereoisomers. As shown in the following stereodrawings, only three stereoisomers exist for this compound. The ds isomer is achiral (meso) because it and its mirror image are superposable. An alternative way to identify the ds isomer as achiral is to notice that it possesses a plane of symmetry that bisects the molecule into two mirror halves. The trans isomer is chiral and exists as a pair of enantiomers. 

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