2-Butanol, synthesis from butene

The first asymmetric synthesis to achieve >90% optical yield was Brown s hydroboration of cis alkenes with diisopinocampheylborane (IpC2BH, Figure 7.10) in 1961 [130,131], The reagent was prepared by hydroboration of a-pinene of 90% ee 2-butanol obtained from hydroboration/oxidation of cw-2-butene had an optical purity of 87%, indicating an optical yield of 90%. ci5-3-Hexene was hydroborated in -100% optical yield. Since then, simple methods for the enantiomer enrichment of lpc2BH (and IpcBH2) have been developed [132-134], and enantioselectivities have been evaluated more carefully with the purified material. For example, lpc2BH of 99% ee affords 2-butanol (from cw-2-butene) in 98% ee and 3-hexanol (from ci5-3-hexene) in 93% ee, both determined by rotation (see Table 7.6, entries 1 and 5) [132]. ... 

An example of a specialty olefin from an amyl alcohol is Phillips Petroleum s new process for 3-methyl-1-butene (used in the synthesis of pyrethroids) from the catalytic dehydration of 3-methyl-1-butanol (21,22). The process affords 94% product selectivity and 94% alcohol conversion at 310°C and 276 kPa (40 psig). 

Furalazine, Acetylfuratrizine, Panfuran-S. Heating nitrovin in butanol or dimethylformamide at 100—130°C affords furalazine, 6-[2-(5-nitro-2-furanyl)ethenyl]-l,2,4-triazine-3-amine (34). An improved synthesis originates with 5-nitro-2-furancarboxaldehyde and acetone, proceeds through 4-(5-nitro-2-furanyl)-3-buten-2-one followed by a selenium dioxide oxidation to the pymvaldehyde hydrate, and subsequent reaction with aininoguariidine (35). Furalazine, acetylfuratrizine (36), and the A[-A/-bis(hydroxymethyl) derivative, Panfuran-S, formed from the parent compound and formaldehyde (37), are systemic antibacterial agents. 

The first substrate which was asymmetrically hydroborated using IPC2BH was c/s -2-butene, and the enantiomeric purity of the product 2-butanol (87% ee) obtained in this preliminary experiment was spectacular (eq 2), since Ipc2BH was made from a-pinene of low optical purity. This reaction represents the first nonenzymatic asymmetric synthesis for achieving high enantioselectivity. Its discovery marked the beginning of a new era of practical asymmetric synthesis obtained via reagent control. ... 

Remark. Pentanols or amyl alcohols, and more specifically 1-pentanok 2-methyl 1-butanol, and 3-methyl 1-butanol, do not enjoy the industrial importance of the above alcohols. They are prepared by Oxo synthesis and hydrogenation from n-butenes and isobutene. They are used as solvents and their esters as perfumes. 

While the four-center transition structure for BH3 addition is a widely used model, other reaction pathways have also been considered. In a synthesis of optically active (-)-l-butanol-l-d, Streitwieser and co-workers used the optically active borane formed from diborane and (-l- )-a-pinene (R2BH) to carry out the hydroboration-oxidation of (Z)-l-butene-l-d. To explain the observed stereochemistry of the reduction, they proposed that hydroboration involves a n complex between R2BH and the alkene (Figure 9.41). Note the close resemblance of such a complex to the cyclic structures... 

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