Nitroalkanes. Roberto BalliniЧитать онлайн книгу.
conjugated nitroalkenes is an important goal and a variety of efficient procedures have been reported [31–36]; however, they seem to be restricted to the reduction of nitrostyrene derivatives. Thus, a survey of the most representative examples is reported in Table 1.4.
1.4.3 Aldehyde Reductive Nitromethylation
Several decades ago, Wollemberg and Miller developed a useful procedure for the preparation of primary nitroalkanes with an extra atom beginning from aldehydes [37]. The starting point is the nitroaldol (Henry) reaction (Scheme 1.17) of an aldehyde with nitromethane, catalyzed with KF and in the presence of i-PrOH as solvent. The formed nitroalkanol is acetylated (acetic anhydride in the presence of 4-dimethylaminopridine as catalyst) and treated with sodium borohydride affording the desired nitroalkane via “one-pot” acetic acid-elimination and C=C double bond reduction.
So, this procedure offers the opportunity to increase the chain length of the starting aldehyde.
Table 1.3 Reduction of nitroalkenes with NaCNBH3 (selected examples).
|
|
||
|---|---|---|
| Nitroalkene | Nitroalkane | Yield (%) |
|
|
|
79 |
|
|
|
74 |
|
|
|
70 |
|
|
|
78 |
|
|
|
78 |
|
|
|
69 |
1.5 Nitration of Alkanes
In contrast with the nitration of aromatic hydrocarbons that can easily performed using nitric acid in the presence of sulfuric acid, the selective nitration of aliphatic hydrocarbons is very difficult due to the exceeding low reactivity of the latter.
Currently, nitration reactions of aliphatic hydrocarbons are carried out at fairly high temperature using nitrogen dioxide or nitric acid, thanks to a free radical process, involving C—H bond homolysis [38]. Often, under such temperature conditions higher alkanes undergo also cleavage of the C–C skeleton. Thus, Ishii and coworkers [39] developed a milder method for the nitration of light alkanes and alkyl side-chain aromatic compounds with NO2 and HNO3 under N-hydroxyphthalimide (NHPI) or N-acetoxyphtalimide (NAPI) catalysis (Table 1.5).
1.6 Metal-Catalyzed Alkylation or Arylation of Nitroalkanes
Commercially available nitroalkanes can be used as precursors of more complex structures through their alkylation or arylation, performed under metal catalysis.
Table 1.4 Stereoselective reduction of nitroalkenes (selected examples).
|
|
||
|---|---|---|
| Substrate | Reducing system | Yield (%), (ee) |
|
|
Baker’s yeast, EtOH·H2O [33] | 91 (S, 12%) |
|
|
Baker’s yeast, EtOH·H2O [33] | 72 (S, 12%) |
|
|
CuF2/PhSiH3, (R)(S)-JOSIPHOS, PHMS/PhMe·H2O [35] | 52 (R, 90%) |
|
|
CuF2/PhSiH3, (R)(S)-JOSIPHOS, PHMS/PhMe·H2O [34] | 88 (R 92%) |
|
|
CuO-t-Bu/PhSiH3, (S)(R)-JOSIPHOS, PMHS/PhMe·H2O [34] | 55 (S, 72%) |
|
|
CuO-t-Bu/PhSiH3, (S)(R)-JOSIPHOS, PMHS/PhMe·H2O [34] | 72 (S, 90%) |
|
|