从烯烃制备醇，也是一个常用的方法，最简单的为烯烃强酸水解，但此方法常常对于复杂的底物是无法应用的；目前一般是通过硼氢化反应得到相应的醇。烯烃羟卤反应可以得到邻卤代醇；烯烃双羟基化可以得到邻二羟基化合物；烯烃羟胺化反应可以邻氨基醇；γ或δ羟基烯烃通过 Kennedy 氧化环合反应得到相应的 2-羟甲基呋喃和吡喃；通过Baylis-Hillman 反应可得到羟基的不饱和酯或腈等。

1、 硼氢化反应

  Alcohols could be obtained mostly by the reduction of the corresponding carboxylic acids, esters, ketones (including CBS asymmetrical reduction) and aldehydes, or by the hydrolysis of halides. Also there is another method by which the desired alcohols also could be obtained, e.g., hydroboration and oxidation of the corresponding alkenes. This classic reaction is often carried out in research labs and it is relatively easy in terms of its operation.

    The syn-addition of hydroboranes to alkenes occurs with predictable selectivity, wherein the boron adds preferentially to the least hindered carbon. This selectivity is enhanced if sterically demanding boranes are used. More specifically, the boron atom usually adds to the terminal carbon if a terminal alkene is used as the substrate. 

      The product boranes may also be used as starting materials for other reactions, such as Suzuki Couplings.

     Coupling the hydroboration with a subsequent oxidation of the new-formed borane yields anti-Markovnikov alcohols. The hydroboration/oxidation sequence constitutes a powerful method for the regio- and stereoselective synthesis of alcohols.

Mechanism

The selectivity of the first addition of borane can be relatively low:

  The subsequent additions are more selective as the steric bulk increases, and anti-Markovnikov selectivity predominates in the end:

Oxidation with hydrogen peroxide leads to alcohols:

   Sterically demanding boranes offer enhanced selectivity. One example of a sterically demanding borane (9-BBN) is generated by the double addition of borane to 1,5-cyclooctadiene:

    The reactivity and selectivity of the borane reagent may be modified through the use of borane-Lewis base complexes.

Experimental Procedure

   A specific example of hydroboration modified by use of borane-Lewis base complexes is demonstrated as below.

Procedure:

  Hydroboration of Representative Olefins Using Dioxane-BH2Cl. Hydroboration of representative olefins, such as 1-octene, 1-decene, styrene, R-methylstyrene, 2-methyl-1-pentene, cis-4-methyl-2-pentene, 2-methyl-2-butene, â-pinene, cyclohexene,R-pinene, 3-carene, 1-phenyl-2-methyl-1-propene, 2,3-dimethyl-2-butene, and

1,2-dimethylcyclopentene, with dioxane-BH2Cl was carried out in dioxane and dichloromethane solvents. The procedure followed for all the olefins in both the solvents are same. The procedure followed for 1-decene in dichloromethane is representative.

     An oven-dried 50 mL round-bottom flask provided with a septum inlet and stirring bar was cooled to 0 °C under nitrogen. The flask was charged with dioxane-BH2Cl in dichloromethane (8.7 mL, 5 mmol). To this was added 1-decene (1.4 g, 10 mmol). The final solution is 0.5 M in BH2Cl and 1.0M in 1-decene. Monitor of the reaction by 11B NMR showed the completion of the reaction after 15 min. The reaction mixture was treated with slow addition of water followed by the addition of sodium hydroxide (7.0 mL,3 M, 21 mmol). Methanol (3.0 mL) was added followed by the slow addition of hydrogen peroxide (6 mmol), and the contents were further stirred at room temperature (3 h) and 40 °C (1 h) to ensure complete oxidation. The organic compound was extracted into diethyl ether. Drying and evaporation of the solvent provided essentially pure 1-decanol in 98% (by GC) isolated 1.48 g, 95% yield.

      An efficient way to access of aromatic ketones is the Friedel-Crafts acylation reaction, which has been known for decades and proved to be practical in small and large scale reactions. Although numerous methods to achieve Friedel-Crafts acylation are known, newer methods continue to attract attention for their experimental simplicity and effectiveness.