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α ‐Amino Acids with Metallocenyl Side Chains
Author(s) -
Dialer Harald,
Polborn Kurt,
Ponikwar Walter,
Sünkel Karlheinz,
Beck Wolfgang
Publication year - 2002
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20020201)8:3<691::aid-chem691>3.0.co;2-d
Subject(s) - chemistry , cyclopentadienyl complex , racemization , lithium (medication) , reagent , enantiomer , stereochemistry , hydrolysis , medicinal chemistry , catalysis , organic chemistry , medicine , endocrinology
A straightforward method for the synthesis of enantiomerically pure bis(valine)metallocenes is presented. Derivatives of lithium cyclopentadienylvaline 1 a, b were obtained by addition of the ( R) ‐ or ( S )‐Schöllkopf reagents to 6,6‐dimethylfulvene as single enantiomers and gave with FeCl 2 or [RuCl 2 (dmso) 4 ] the chiral metallocenes [Fe{C 5 H 4 ‐CMe 2 ‐[C 4 H 2 N 2 (OMe) 2 i Pr]} 2 ] ( 2 a, b ) and [Ru{C 5 H 4 ‐CMe 2 ‐[C 4 H 2 N 2 (OMe) 2 i Pr]} 2 ] ( 3 a, b ). Complex 2 b was hydrolyzed to the ferrocenylene‐bis(valine‐methylester) [{Fe[C 5 H 4 ‐CMe 2 ‐CH(NH 3 + )COOMe] 2 } 2+ (Cl − ) 2 ] ( 7 ) without racemization. Complex 7 could be used as ligand and was treated with [{Cp*IrCl 2 } 2 ] to afford [Fe{C 5 H 4 ‐CMe 2 ‐CH(COOMe)(NH 2 ‐IrCp*Cl 2 )} 2 ] ( 10 ). The reactions of 1 with CoCl 2 , [Re(CO) 5 Br], [{(cod)RhCl 2 } 2 ] (cod=1,5‐cyclooctadiene) or [Cp*MCl 3 ] (M=Ti, Zr) gave the cyclopentadienyl complexes [{Co{C 5 H 4 ‐CMe 2 ‐[C 4 H 2 N 2 (OMe) 2 i Pr]} 2 } + I − ] ( 11 ) and [Re{C 5 H 4 ‐CMe 2 ‐[C 4 H 2 N 2 (OMe) 2 i Pr]}(CO) 3 ] ( 13 ), [(C 8 H 12 )Rh{C 5 H 4 ‐CMe 2 ‐[C 4 H 2 N 2 (OMe) 2 ( i Pr)]}] ( 14 ), [{Rh{C 5 H 4 ‐CMe 2 ‐[C 4 H 2 N 2 (OMe) 2 ( i Pr)]}I} 2 ( μ ‐I) 2 ] ( 15 ), [Cp*Cl 2 Ti{C 5 H 4 ‐CMe 2 ‐[C 4 H 2 N 2 (OMe) 2 ( i Pr)]}] ( 16 ), and [Cp*Cl 2 Zr{C 5 H 4 ‐CMe 2 ‐[C 4 H 2 N 2 (OMe) 2 ( i Pr)]}] ( 17 ), with chiral valine derivatives as substituents on the cyclopentadienyl ring and with excellent diastereoselectivities. Also the Seebach reagent (Boc‐BMI) or O′Donnell reagent could be added to 6,6‐dimethylfulvene to give the lithium cyclopentadienides Li[C 5 H 4 ‐CMe 2 ‐{C 3 H 2 ( t Bu)( N ‐Boc)(NMe)O}] ( 18 ) and Li[C 5 H 4 ‐CMe 2 ‐CH(NCPh 2 )(COOEt)] ( 21 ), which formed the ferrocene derivatives [Fe{C 5 H 4 ‐CMe 2 ‐[C 3 H 2 ( t Bu)(N‐Boc)(NMe)O]} 2 ] ( 19 ) and [Fe{C 5 H 4 ‐CMe 2 ‐CH(NCPh 2 )(COOEt)} 2 ] ( 22 ). The stable cobaltocinium cation in 11 and the complex 19 could be hydrolyzed to the metallocenes 12 and [Fe{C 5 H 4 ‐CMe 2 ‐CH(NH 3 + )(COO − )} 2 ] ( 20 ) with two valines in the 1,1′‐position. The structures of 2 a, b, 11, 15 , and 16 were determined by X‐ray diffraction and confirm the diastereomeric purity of the compounds.