[ C O X T R I B U I ' I O N FROM T H E
DEPARTMENT OF
CHEMISTRY, C O L U M B I A L T L I V E R S I l\i
1
Stereospecific Hydrogenation of a-Pinene Derivatives
'r.
BY (;. W. E I G E X ~ C ~AXD X XILclariisplatinum catalyst yielded oiily one of twt-o possible diastereoisomers. These obserx ations prompted us t-, extend the hydrogenation studies to several other a-pinene derivatives, including inyrter'ic acid ( I a ) , myrtenol (Ib), nopol (IC) and diethyl nopylmalonate (Id In each case, the hydrogenation proceeded iii highly stereospecific manner to give a single identifiable product. It has been recognized for some time' that steric factors may play a dominant role in bringing about prefrrential adsorption of a substrate on a catalytic surface, and thus determine the configuration of the product formed. The application of these concepts to situations in..-olving many coniplex molecules has proved to be very valuable.' In the present study i t way assumed from the outset t h a t effective adsorption ( i . ,~one which could lead to facile hydrogenation) of an a-pincne nucleus a t a catalytic surface is determiiiecl largely by the relative steric requirements of the meth!-lene and isopropylidene bridges. .'ts a result, reduction under the mild conditions enip!oyed here should lead to cis addition of hJTdrogei1 overwhelmingly from the methylene bridge side of the molecule as ).
T l . s T m & H & > ; , k c . i t d y s t ,uriacc
l a , I< =
COOH I!,, I< = --CIT,OH I C , It = - C I ~ ~ C H ~ 0 1 1 ltl, I< = . CIS~CH,CII~ C O U C : I l , , ) ~ 113, I< = -COO€I 1113, I1 = -CIIZOH IIc., R = -CH,CHrOII IId, I< = --CI-I,CI~,CHiCoOC.111,), ~
Results frcxii the present siutly arc' iii lull accord with this L-iew. Such a mode of addition o f hydrogen, hm would lead t:, the forniatioii of the therrnod! cally less stable isxner, since there is developed in the primary product a considerable strain due to (1) T'nitdwtcirate Reiearch A (2) Alir?d l', Sloan Research ( 3 ) I < , 7'. Arnold a n d J. S Sh ( I) I I l O 5 i ) . I .[. I
