SynopsisThe enantioselective polymerization of bis(2,2,2-trichloroethyl) trans-3,4-epoxyadipate with 1,4-butanediol using the enzyme porcine pancreatic lipase as a catalyst is described. The polymerization was carried out at ambient temperature in anhydrous ethyl ether. End group analysis provided M , = 5,300 daltons, whereas GPC provided M , = 7,900 daltons for the polymer. The unchanged (+)-enantiomer of the diester was shown to have an enantiomeric purity of > 95% by proton NMR in the presence of the chiral shift reagent Eu(hfc),. The stereochemical purity of the (-)-polymer was estimated at > 96% by consideration of the amount of the slower reacting enantiomer that could have been incorporated and still attain the observed degree of polymerization (25) when the starting ratio of racemic diester to diol was 2 : 1. Direct determination of the stereochemical purity of the polymer using Eu(hfc), was unsuccessful. Similar studies on polymer having random stereochemical orientations of the epoxide showed that such polymers do not behave as if they are racemic in the presence of the shift reagent. The polymer required for the latter studies was prepared by epoxidation of the product from enzyme catalyzed polymerization of bis(2,2,2-trichloroethyl) trans-3-hexenedioate with 1,4-butanediol.

SynopsisEnzyme-catalyzed preparation of polymers offers several potentially valuable advantages over the usual polymerization procedures. (1) Such polymerizations may allow the polymer to retain functionality that would be destroyed under normal polymerization conditions. (2) The selectivity provided by enzyme catalysts may permit polymers, including optically active polymers, to be prepared that are either not accessible or accessible only with difficulty by other methods. (3) The characteristics of the enzyme and the mild polymerization conditions may permit formation of polymers having highly regular sizes and backbone structures. This report describes the first successful use of an enzyme-catalyzed polycondensation to prepare a chiral (AA-BB), polyesters of more than a few repeat units. Polymerization of bis(2,2,2-trichloroethyl) alkanedioates (BB) with diols (AA) using the enzyme porcine pancreatic lipase (PPL) as a catalyst is detailed. The polycondensations were carried out at ambient temperature in anhydrous, low polarity organic solvents such as ether, THF, and methylene chloride. End group analysis by NMR provided M,, values of 1300-8200 daltons while GPC provided M , values of 2800-14900 daltons for the polymers. Based on proton NMR spectra obtained during the polymerization, relatively rapid formation of an AA-BB "dimer" and an AA-BB-AA " trimer," slower formation of a BB-AA-BB "trimer," and subsequent condensation of these to give higher polymers are suggested to be components of the polymerization mechanism.

Asymmetric Homogeneous Hydrogenation with Rhodium(I) Complexes of Chiral Phosphines Sir:There has been recent interest in asymmetric hydrogenations catalyzed by soluble rhodium catalysts of the Wilkinson type.1-4 For example, asymmetric hydrogenation of -phenylacrylic acid was accomplished (18) NSF Undergraduate Summer Research Participant, 1969.

Lee, Morrow, and Rapoport N-methylnipecotic acid (6) to l-methyl-3-methylene-2piperidone (7) has been reported.4 0 H 5 CH3 6CH,

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