Alcohols secondaiy

This method is also effective for the protection of primary an i secondaiy alcohols. 

PvCl, Pyr, 0-75°, 2.5 days, 99% yield. In general, such extended reaction times are not required to obtain complete reaction. This is an excellent reagent for selective acylation of a primary alcohol over a secondaiy alcohol. "... 

In cases where two 1,2-acetonides are possible, the thermodynamically favored one prevails. Secondaiy alcohols have a greater tendency to form cyclic acetals than do primaiy alcohols,but an acetonide from a primaiy alcohol is preferred over an acetonide from two trans, secondaiy alcohols. 

Secondaiy alcohols may be prepaied by two different combinations of Grignaid reagent and aldehyde ... 

CH3Q—CH — p-Methoxybenzaldehyde Ketones yield secondaiy alcohols ... 

Condensation of piperazine with 2-methoxytropone gives the addition-elimination product 12 [2]. Alkylation of the remaining secondary amino group with bromoketone 13, itself the product from acylation of dimethyl catechol, gives aminoketone 14. Reduction of the carbonyl group with sodium borohydride leads to secondaiy alcohols 15 and 16. Resolution of these two enantiomers was achieved by recrystallization of their tartrate salts to give ciladopa (16) [3],... 

Secondaiy alcohol 15b presumably is isomerized to enol 28, but at temperatures of 70°C the laber is quickly converted to the most stable keto form (16b), the observed product. Interesbngly, silylation of the alcohol (29) allows for a mild and complete isomerizabon to ( )-30 at room temperature, confirming that an alcohol OH group somehow slows the first isomerizabon step. However, the alcohol... 

The cyclization process can be promoted by using a single electron transfer mediator. Electron transfer from the mediator generates the carbonyl radical-ion away from the electrode surface so that cyclization can occur before there is opportunity for a second electron transfer. Thus reduction of 16, R = Me, in dimethyl-forraaraide at mercury in the presence of tetraethylammonium fluoroborate leads only to conversion of the ketone function to the secondaiy alcohol. However addition of a low concentration of N,N-dimethyl pyrrolidinium fluoroborate alters the course of reaction and the cyclized tertiary alcohol is now formed. This pyrrolidinium salt is reduced at -2.7 V vs. see at mercuiy to yield a complex DMP(Hg5) which is thought to act as a single electron transfer mediator [94]. Cyclization can... 

Ac20, Pyr, 20°, 12 h, 100% yield.1 This is one of the most common methods for acetate introduction. By running the reaction at lower temperatures good selectivity, pan be achieved for primaiy alcohols over secondaiy alcohols.2 Tertiary alcohols are generally not acylated under these conditions. 

Bu4N+F, THF, 0°, 1 h, 52-95% yield.4 A primary alcohol protected as the r-butyldimethylsilyl ether is cleaved under these conditions, but a similarly protected secondaiy alcohol is stable. 

An acid catalyst is used to promote loss of water, and in dilute H2SO4 or HC1 the absence of good nucleophiles ensures that substitution does not compete. Under these conditions, the secondaiy alcohol cyclohexanol gives cyclohexene,... 

With the catalytic system secondaiy alcohols are still oxidized quickly (Scheme 2) and in excellent yield with 2 equiv. of peracetic acid at 0 C. Primary alcohols are also reported to be oxidized to aldehydes in good yields, but details have not been given. 

Ammonium cerium(IV) nitrate or cerium(IV) sulfate will catalyze the selective oxidation of secondaiy alcohols with sodium bromate as cooxidant, in this case remote C—C double bonds interfere, but 1,2-diols are not cleaved. It has been found that sodium bromite in aqueous acetic acid will act as a selective oxidant for secondary mary diols without the need for other catalysts (Scheme 21). ... 

Alcohols are among the most versatile of all organic compounds. They occ. widely in nature, are important industrially, and have an unusually he chemistry. The most important methods of alcohol synthesis start with carbonyl compounds. Aldehydes, ketones, esters, and carboxylic acids are reduced by reaction with either NaBH,i or LiAIH4. Aldehydes, esters, and carboxylic acids yield primary alcohols (RCHgOH) on reduction ketones yield secondaiy alcohols (R CHOH). 

Alcohol has probability 0.9 Primaiy alcohol has probability 0.01 Secondaiy alcohol has probability 0.99 Tertiaiy alcohol has probability 0.01 Phenol has probability 0.01... 

Anodier reagent which undoubtedly will prove to be of real synthetic value is periodinane, which is an excellent, mild oxidant fcnr (uiinaiy (and secondaiy) alcohols. This reagent is scussed further in Sec-timi 2.9.3. 

The same concept was applied to BINOL ligands. Abdi et al. described the synthesis of silica-supported chiral BINOL 55 and its evaluation in enantioselective all lation of various aldehydes with diethylzinc (Scheme 7.29). Good to high enantioselectivities (up to 94% enantiomeric excess) for the obtained chiral secondaiy alcohols were measured. Once again, the supported BINOL catalyst has been reused in several catalytic runs without a significant drop in enantioselectivity. 

One of the typical applications of chiral DMAP catalysts is the atylative kinetic resolution of racemic secondary alcohols. Two landmark catalj ts, planer chiral DMAP catalyst 7 and chiral bicyclic PPY catalyst 10, were developed independently by Fu and Kawabata, respectively (Schemes 22.1 and 22.2). Catalysts 7 showed excellent properties as chiral nucleophilic catalysts. In the presence of 2 mol% of 7b, a variety of racemic secondaiy alcohols possessing aryl (or vinyl) and allg l groups such as 8 and 9 were kinetically resolved with acetic anhydride to give the acetates and the recovered starting materials in high enantioselectivity (s = 12-52) (Scheme 22.1). ... 

Scheme 22.1 Acylative kinetic resolution of racemic secondaiy alcohols with Fu s planar-chiral DMAP catalysts.

SeCOndaiy Alcohols. Reactions 13.10and 13.11 give the general reaction and a specific example. 

Table 2. Ruthenium-TEMPO catalysed oxidation of secondaiy alcohols to the conesponding...

Gagosz reported the 5-endo hydroxy- and alkoi -cyclisation of 1,5-enynes to afford functionalised cyclopentenes. Complex XXIV (1 mol%) was used as catalyst, the reaction proceeded at room temperature and the final products were isolated in moderate to excellent yields. Primary and secondaiy alcohols, phenols and water were successfully used as nucleophiles and incorporated in the products (Scheme 16.67). ... 

---