The First Direct Evidence for a Cram Chelate

Reetz, Manfred T.; Hüllmann, Michael; Seitz, Tobias

doi:10.1002/anie.198704771

Cited by 56 publications

(19 citation statements)

References 9 publications

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“…The possibility of chelation of protected α-hydroxy aldehydes and ketones to Lewis acids has been examined by NMR spectroscopy6,8,75-78 and X-ray crystallography 79. Ketones are usually preferred for these studies over aldehydes due to their greater stability in the presence of Lewis acids.…”

Section: Resultsmentioning

confidence: 99%

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Overriding Felkin Control: A General Method for Highly Diastereoselective Chelation-Controlled Additions to α-Silyloxy Aldehydes

2010

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According to the Felkin-Anh and Cram-chelation models, nucleophilic additions to α-silyloxy aldehydes procees through a non-chelation pathway due to the steric and electronic properties of the silyl group, giving rise to Felkin addition products. Herein we describe a general method to promote chelation-control in additions to α-silyloxy aldehydes. Dialkylzincs, functionalized dialkylzincs, and (E)-disubstituted, (E)-trisubstituted, and (Z)-disubstituted vinylzinc reagents add to silyl-protected α-hydroxy aldehydes with high selectivity for chelation-controlled products (dr of 10:1 to >20:1) in the presence of alkylzinc halides or triflates, RZnX. With the high functional group tolerance of organozinc reagents, the mild Lewis acidity of RZnX, and the excellent diastereoselectivities favoring the chelation-controlled products, this method will be useful in the synthesis of natural products. A mechanism involving chelation is supported by 1) NMR studies of a model substrate, 2) a dramatic increase in reaction rate in the presence of an alkylzinc halide, and 3) higher diastereoselectivity with larger alkyl substituents on the α-carbon of the aldehyde. This method provides access to chelation-controlled addition products with high diastereoselectivity previously unavailable using achiral organometallic reagents.

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Section: Resultsmentioning

confidence: 99%

“… a NMR studies by Reetz (entry 1)75 and Eliel and Frye (entries 2–6),20 NA= Not applicable, NR= not reported, Δ values reported in ppm. …”

Section: Figures and Tablesmentioning

confidence: 99%

Overriding Felkin Control: A General Method for Highly Diastereoselective Chelation-Controlled Additions to α-Silyloxy Aldehydes

2010

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“…Thus, methyl iodoglycoside 7 was subjected to the optimised Vasella reductive amination conditions, but with the use of diphenylmethyl amine as the amine nucleophile (Scheme ). This resulted in the formation of alkenylamines 11 a and 11 b in 85% total yield and in an, albeit modest, improved 3:2 ratio, in favour of the anti‐Felkin product . Formation of the desired product was evidenced by HRMS ( m/z calcd.…”

Section: Resultsmentioning

confidence: 64%

Diastereoselective Carbamate Annulation for the Synthesis of 2,5‐Dideoxy‐2,5‐iminoglycitols

et al. 2017

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A combination of the Vasella‐reductive‐amination and carbamate annulation reactions was applied on a ketose starting material for the diastereoselective total synthesis of 2,5‐dideoxy‐2,5‐imino‐glycitols. The synthesis of 2,5‐dideoxy‐2,5‐imino‐l‐iditol (4) was particularly expedient (6 steps and 18% overall yield) as the route minimises the use of protecting groups, thereby reducing the number of synthetic steps and increasing the overall yield. The Vasella reductive amination methodology could be readily applied to the amination of ketones, albeit with moderate diastereoselectivity. However, the I2‐mediated carbamate annulation strongly favours the formation of pyrrolidines with the 2,5‐trans and 4,5‐cis relationships. The highly diastereoselective carbamate annulation thus provided a general means by which to synthesise 2,5‐dideoxy‐2,5‐imino‐glycitols of defined stereochemistry.

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“…Hinweise auf eine positive Partialladung des Methinkohlenstoffatoms in Gegenwart des Titankomplexes 3 liefern die in CD 3 CN aufgenommenen 13 C‐NMR‐Spektren von 1:1‐Gemischen aus den Indanderivaten 1 a und 1 b und dem Komplex (Schema ). Ähnliche Tieffeldverschiebungen resultieren auch, wenn die Substrate 1 a und 1 b in Gegenwart von äquimolaren Mengen Titantetrafluorid vermessen werden 15…”

Section: Methodsunclassified

Titan(IV)‐katalysierte dynamisch‐kinetische asymmetrische Umwandlung von Alkoholen, Silylethern und Acetalen unter Kohlenstoff‐Allylierung

Braun

Kotter

2004

Angewandte Chemie

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Hohe Ausbeuten und gute Enantioselektivität werden durch eine dynamisch‐kinetische asymmetrische Umwandlung, in der die C‐O‐Bindung von Alkoholen, Silylethern und Acetalen durch eine C‐C‐Bindung ersetzt wird, erzielt. Beispielsweise wird mithilfe eines chiralen, Lewis‐sauren Titan(IV)‐Komplexes der racemische Indanylsilylether 1 in den Kohlenwasserstoff (S)‐2 überführt (siehe Schema).

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The First Direct Evidence for a Cram Chelate

Cited by 56 publications

References 9 publications

Overriding Felkin Control: A General Method for Highly Diastereoselective Chelation-Controlled Additions to α-Silyloxy Aldehydes

Overriding Felkin Control: A General Method for Highly Diastereoselective Chelation-Controlled Additions to α-Silyloxy Aldehydes

Diastereoselective Carbamate Annulation for the Synthesis of 2,5‐Dideoxy‐2,5‐iminoglycitols

Titan(IV)‐katalysierte dynamisch‐kinetische asymmetrische Umwandlung von Alkoholen, Silylethern und Acetalen unter Kohlenstoff‐Allylierung

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