Cyclopentyl methyl ether

A BINOL-dimethylaminopyridine hybrid was seen to be efficient in mediating the MBH reaction (Table 5.14) [96], with optimal reaction conditions being found as —15 °C with a mixed solvent system consisting of toluene and cyclopentyl methyl ether (CPME) in a 1 9 ratio. The reaction was sensitive to the structure of the catalyst 112, the position of the Lewis base attached to BINOL, the substitution pattern of the amino group, and the length of the spacer. It should be noted that the bulky i-Pr substituent on the amino group showed the best selectivity and kinetic profile (Table 5.14, entry 5) [98]. (For experimental details see Chapter 14.10.4). 

Frequently, several different routes can potentially be used to synthesize a desired compound. For example, the following two routes can be envisioned for the preparation of cyclopentyl methyl ether. Explain which of these two routes you expect to give the higher yield of the desired ether. 

Cyclohexane, Heptane, Toluene, Methylcyclohexane, Methyl t-butyl ether, isooctane 2-MethylTHF, Cyclopentyl methyl ether. Xylenes, DMSO, Acetic acid. Ethylene glycol... 

Cyclopentyl methyl ether (CPME) is another alternative to typical ethereal solvents such as diethyl ether, THF, DME and dioxane. At present it is not bio-sourced but it is mentioned here as it has many advantageous properties as a direct replacement for ethers. Most importantly, the rate of peroxide formation is very slow and therefore, CPME is green in terms of risk avoidance and other criteria. Its use in a range of classical and modern synthetic procedures has been reported. ... 

Seed crystals were also effective for the inclusion complexation of 12 with some other guests. Contact of powdered 12 with gaseous MeOAc and EtOAc for 3 h in the presence of seed crystals of 3 1 inclusion complexes of 12 and MeOAc and EtOAc, respectively, led to the corresponding inclusion complexes in quantitative yields. A pseudo-seed crystal is also effective. For example, contact of powdered 12 with ethyl ether vapor for 3 h in the presence of a seed crystal of the 3 1 complex of 12 and MeOAc gave the 3 1 complex 82 but not 83. Similar conctact of powdered 12 with ethyl ether vapor for 12 h in the presence of a seed crystal of the 1 2 complex of 12 and cyclopentyl methyl ether gave the 1 2 complex 83 but not 82 [47]. 

The upper route, using the conjugate base of cyclopentanol and methyl iodide, will yield only the substitution product because methyl iodide cannot give an elimination product. In the case of the lower route, with bromocyclopentane (a secondary substrate) and methoxide anion (a strong base), E2 elimination will predominate. Therefore, the upper route will give the higher yield of cyclopentyl methyl ether. 

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