Remarkable effect of lithium bromide in the enantioselective protonation with α-sulfinyl alcohols

Tetrahedron Letters

Volumn 39, Issue 20, 1998, Pages 3277-3280

  Asensio, Gregorio ^a   Aleman, Pedro A ^a   Domingo, Luis R ^a   Medio Simón, Mercedes ^a  

^a UNIVERSITY OF VALENCIA   (Spain)

Author keywords

[No Author keywords available]

Indexed keywords

ALCOHOL DERIVATIVE; LITHIUM BROMIDE; LITHIUM DERIVATIVE; UNCLASSIFIED DRUG;

ARTICLE; MODEL; PROTON TRANSPORT; STEREOCHEMISTRY;

EID: 0032516320     PISSN: 00404039     EISSN: None     Source Type: Journal    
DOI: 10.1016/S0040-4039(98)00469-9     Document Type: Article

References (23)

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13. 2a,b we have obtained similar optical yields when the reactions were quenched at -50 or at 0° C.
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16. 2a,b only when the enolate was generated from 2b and methyllithium complexed with LiBr . Generation of enolates 3a and 3b: A diethyl ether solution of methyllithium 1.6 M or methyllithium as complex with lithium bromide 1.5 M (1.1 mmol) was added to neat 2a at room temperature. The mixture was stirred for 1h and then diethyl ether was added (9 ml). Generation of enolates 3c and 3d: To a stirred solution of 2b (1.0 mmol) in diethyl ether (9 ml) at 0° C was added an ether solution of methyllithium 1.6 M or methyllithium as complex with lithium bromide 1.5 M (1.1 mmol) and the mixture was stirred at room temperature for 30 mins. General procedure for protonation: The lithium enolate solution (10 ml) at -75 ° C was slowly added to a solution of (S,Rs)-1 (2.5 mmol) in the appropriate solvent (15 ml) and temperature. The mixture was stirred (1.5 h) at the same temperature and then gradually warmed up to the quenching temperature (temperature increase approximately 1.2 °C/ min). The reaction mixture was treated with the phosphate buffer (pH : 7.2) and extracted with hexane. The residue was purified by column chromatography to give (R)-4 (90-94% yield).
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