Iron-Mediated Allylic Substitution Reactions with Chirality Transfer. Stereochemistry of the Formation of Diastereo- and Enantiomerically Enriched Olefinic and Allylic Tetracarbonyl Iron Complexes
详细信息 查看全文
- 作者：Dieter Enders ; Bernd Jandeleit ; Stefan von Berg ; Gerhard Raabe ; and Jan Runsink
- 刊名：Organometallics
- 出版年：2001
- 出版时间：October 15, 2001
- 年：2001
- 卷：20
- 期：21
- 页码：4312 - 4332
- 全文大小：285K
- 年卷期：v.20,no.21(October 15, 2001)
- ISSN：1520-6041
文摘
(E)-Configurated allylic ligands (S)-6a-f and (S)-8, bearing a leaving group at C(3) (allylicposition) and an electron acceptor substituent at C(1), were synthesized from enantiopure(S)-ethyl lactate [(S)-1]. Complexation with Fe2(CO)9 (13) afforded diastereomeric mixturesof their (
2-alkene)tetracarbonyliron(0) complexes 14a'/a' '-f'/f' ' (acceptor group, Acc = SO2Ph) and 15'/' ' (Acc = CO2Me) (48% - quant.; de < 3-70%), each diastereomer in enantiopureform (Note: descriptors ' and ' ' denote major and minor diastereomer). Synthetically usefulresults were obtained for allylic ligands bearing a benzylic protecting group [(S)-6a and (S)-8] and using hexane or diethyl ether as solvent (14a'/a' ': quant., de = 70%; 15'/' ': 75-88%,de = 10-16%). Complexes 14a'/a' ' were fractionally crystallized, and their molecularstructures were determined by X-ray diffraction, allowing for an assignment of the absoluteconfigurations of complexes 14a'/a' '-f'/f' ' and 15'/' '. "W"-shaped complexes 14a', 15' ' (
-exo-14,15) were expected to yield syn-Me,syn-Acc-configured and "S"-shaped complexes 14a' ',15' (-endo-14,15) accordingly anti-Me,syn-Acc-configured cationic complexes 18 and 19 upontreatment with HBF4. Complex 14a' (de = ee > 99%) reacted quantitatively to the syn-Me-substituted (3-allyl)tetracarbonyliron(1+) complex 18' (syn-Me,syn-SO2Ph-18) (syn-Me/anti-Me > 99:1, ee > 99%). Diastereomeric mixtures of complexes 14a'/a' ' gave mixtures ofcomplexes 18', 18' ' (anti-Me,syn-SO2Ph-18) and ent-18' ' (ent-syn-Me,syn-SO2Ph-18). Conversion of complex 14a' ' to 18' ' or complex 18' ' itself was subjected to an anti-Me 
syn-Meisomerization process, yielding eventually a diastereomeric mixture of complexes 18' ' andent-18' ', thus lowering the overall enantiomeric purity of syn-Me,syn-SO2Ph-substitutedcomplexes 18. Conversion of a mixture of 15'/' ' (de = 10%) to cationic complexes 19'/' ' didnot exhibit significant anti-Me syn-Me isomerization (syn-Me:anti-Me = 1:1.19, ee > 96%for both diastereomers). Nucleophilic anti-addition of silyl enol ether 20 to complex 18' orsilyl ketene acetal 21 to a complex mixture 19'/' ' afforded enantiopure alkenyl sulfone (R)-23 or ester (S)-24 (82% - quant., ee >96 to >99%). Addition to a complex mixture containing18', 18' ', and ent-18' yielded 23, albeit with lower enantiomeric purity (ee = 59-66%). Thechirality transfer process of the iron-mediated allylic substitution proceeds with overallretention (double inversion) of stereochemistry with respect to the stereogenic center of thestarting materials, conservation of (E)-double bond geometry, and complete 
-regioselectivityfor the nucleophilic addition reactions. Differences of configurative stability of the anti-configured Me groups in the cationic 
-allyl complexes 18' ' and 19' were found requiringappropriate consideration if used in stereocontrolled organic synthesis.
2-alkene)tetracarbonyliron(0) complexes 14a'/a' '-f'/f' ' (acceptor group, Acc = SO2Ph) and 15'/' ' (Acc = CO2Me) (48% - quant.; de < 3-70%), each diastereomer in enantiopureform (Note: descriptors ' and ' ' denote major and minor diastereomer). Synthetically usefulresults were obtained for allylic ligands bearing a benzylic protecting group [(S)-6a and (S)-8] and using hexane or diethyl ether as solvent (14a'/a' ': quant., de = 70%; 15'/' ': 75-88%,de = 10-16%). Complexes 14a'/a' ' were fractionally crystallized, and their molecularstructures were determined by X-ray diffraction, allowing for an assignment of the absoluteconfigurations of complexes 14a'/a' '-f'/f' ' and 15'/' '. "W"-shaped complexes 14a', 15' ' (-exo-14,15) were expected to yield syn-Me,syn-Acc-configured and "S"-shaped complexes 14a' ',15' (-endo-14,15) accordingly anti-Me,syn-Acc-configured cationic complexes 18 and 19 upontreatment with HBF4. Complex 14a' (de = ee > 99%) reacted quantitatively to the syn-Me-substituted (3-allyl)tetracarbonyliron(1+) complex 18' (syn-Me,syn-SO2Ph-18) (syn-Me/anti-Me > 99:1, ee > 99%). Diastereomeric mixtures of complexes 14a'/a' ' gave mixtures ofcomplexes 18', 18' ' (anti-Me,syn-SO2Ph-18) and ent-18' ' (ent-syn-Me,syn-SO2Ph-18). Conversion of complex 14a' ' to 18' ' or complex 18' ' itself was subjected to an anti-Me syn-Meisomerization process, yielding eventually a diastereomeric mixture of complexes 18' ' andent-18' ', thus lowering the overall enantiomeric purity of syn-Me,syn-SO2Ph-substitutedcomplexes 18. Conversion of a mixture of 15'/' ' (de = 10%) to cationic complexes 19'/' ' didnot exhibit significant anti-Me syn-Me isomerization (syn-Me:anti-Me = 1:1.19, ee > 96%for both diastereomers). Nucleophilic anti-addition of silyl enol ether 20 to complex 18' orsilyl ketene acetal 21 to a complex mixture 19'/' ' afforded enantiopure alkenyl sulfone (R)-23 or ester (S)-24 (82% - quant., ee >96 to >99%). Addition to a complex mixture containing18', 18' ', and ent-18' yielded 23, albeit with lower enantiomeric purity (ee = 59-66%). Thechirality transfer process of the iron-mediated allylic substitution proceeds with overallretention (double inversion) of stereochemistry with respect to the stereogenic center of thestarting materials, conservation of (E)-double bond geometry, and complete -regioselectivityfor the nucleophilic addition reactions. Differences of configurative stability of the anti-configured Me groups in the cationic -allyl complexes 18' ' and 19' were found requiringappropriate consideration if used in stereocontrolled organic synthesis.