Premium
Synthesis of Optically Active Bifunctional Isoprenoid Building Blocks by Rhodium(I)‐Catalyzed Asymmetric Allylamine to Enamine Isomerization
Author(s) -
Schmid Rudolf,
Hansen HansJürgen
Publication year - 1990
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19900730516
Subject(s) - chemistry , isomerization , enamine , bifunctional , allylic rearrangement , allylamine , amination , asymmetric induction , optically active , rhodium , organic chemistry , ligand (biochemistry) , combinatorial chemistry , stereochemistry , catalysis , enantioselective synthesis , biochemistry , receptor , polyelectrolyte , polymer
The application of the known asymmetric allylamine to enamine isomerization methodology to bifunctional C 5 ‐isoprenoid allylic amines of types IId and IIe (Scheme 1) is described. It is shown that a number of such substrates can be isomerized with enantioselectivities of > 90% ee. using cationie Rh 1 complexes containing (6. 6′‐dimethylbiphenyl′2, 2′‐diyl)bis(dipheny phosphine) (BIPHEMP; 9) as asymmetry‐inducing ligand ( Scheme 2, Tables 1 and 2 ). Synthetically most useful is the isomerization of the benzyloxy derivative 10a into the ( E )‐enamine 11a . This isomerization proceeds with very high enantioselectivity (98‐99% ee) and affords, after enamine hydrolysis, the optically active 4‐(benzyloxy)‐3‐methylbutanals (( R )‐ or ( S )‐ 12 ) in chemical yields of ca. 90%. In conjunction, a short synthetic route to the starting material 10a has been developed which has a Pd‐catalyzed amination of isoprene epoxide ( 30 ) as the key step. Thus, convenient and practical access to the optically active aldehydes ( R )‐and ( S )‐ 12 is now at hand. These aldehydes are useful optically active bifunctional building blocks for isoprenoid homologation.