WebIt has been demonstrated that water adds rapidly to the carbonyl function of aldehydes and ketones to form geminal-diol. In a similar reaction alcohols add reversibly to aldehydes and ketones to form hemiacetals (h emi, Greek, half). This reaction can continue by adding another alcohol to form an acetal. WebAn acid catalyst must be used during this reaction because alcohols are weak nucleophiles and would add very slowly under neutral conditions. Under acidic conditions, the oxygen of the carbonyl becomes protonated, increasing the electrophilicity of the carbonyl carbon, speeding up the reaction.
Addition of Alcohols to form Hemiacetals and Acetals
WebCommon reagents for deprotection: acids (TsOH, TFA, HCl etc) with addition of water * Can be selectively converted into Bn or Bz Examples: O HO OMe HO O O Ph NBS, CCl4 BaCO3, reflux O HO OMe HO Br BzO O HO OMe HO NBS, CCl4 BaCO3, reflux O HO OMe HO BzO Br O O Ph (J. Org. Chem. 1969, 34, 1035) O NPhth BnO OR O O MeO NaBH3CN TFA, DMF 90% … WebTSOH, CH3CH2OH (2 equiv) Draw the major product of this reaction. Ignore inorganic byproducts. Assume that the water side product is continuously removed to drive the reaction toward products. O 0 (CH2OH)2, TsOH Draw the major product of this reaction. Ignore inorganic byproducts. H3O+ Draw the major product of this reaction. doj jedi
Chapter 3 Protecting Groups - Utah State University
WebJan 23, 2024 · It has been demonstrated that water adds rapidly to the carbonyl function of aldehydes and ketones to form geminal-diol. In a … WebAddition of a proton (e.g.: p -TsOH, H 2 SO 4) or a Lewis acid leads to a more reactive electrophile. Nucleophilic attack of the alcohol gives a tetrahedral intermediate in which there are two equivalent hydroxyl groups. One of these hydroxyl groups is eliminated after a proton shift (tautomerism) to give water and the ester. WebFeb 4, 2011 · Acetals formed from low boiling alcohols such as methanol or ethanol can be exchanged with higher boiling alcohols under acidic conditions. A method that is often used is the treatment of 1,2-diols with 2,2-dimethoxypropane and an acid catalyst such as pyridinium p-toluenesulfonic acid (PPTS) <2001EJO1865>.Yields are generally very high (> … doj jdis 2043