Roberto Ballini is a Full Professor of Organic Chemistry at the University of Camerino (Italy) and Past President of the Italian Organic Chemistry Division. The scientific activity of Prof. Ballini is mainly dedicated to Organic Synthesis, with particular interest on the chemistry of nitroalkanes that, thanks to their highly chemical versatility, can be easily employed for new generation of C—C single and C=C double bond, for the cleavage of C—C bond, for their conversion into other important functionalities, thus as key building blocks in the synthesis, often under sustainable conditions, of a large variety of important “fine chemicals” such as natural products featuring enhanced biologically activity, pharmaceuticals, etc.
The scientific activities have been evidenced by:
1 More than 250 publications, including more than 20 reviews, mainly dedicated to the chemistry of nitroalkanes.
2 The role of Editor of the Green Chemistry Books: (i) Eco-Friendly Processes and Procedures for the Synthesis of Fine Chemicals (2009) and (ii) Green Synthetic Processes and Procedures (2019); both of Green Chemistry Series of Royal Chemical Society, Cambridge.
3 The preparation, as main author, of four Book chapters on the field of “Nitroalkanes.”
Alessandro Palmieri obtained his Laurea degree cum laude in Chemistry in 2002 at the University of Camerino (Italy) where, five years later, he received the PhD degree in Chemical Sciences. Then, in the period 2007–2010 he held a postdoctoral fellowship and in 2008 he moved, as visiting postdoctoral fellow, to the ITC laboratory at the University of Cambridge (Prof. Steven V. Ley). After the experience as assistant professor (2010–2013), in 2014 he was appointed associate professor in Organic Chemistry at the University of Camerino. Currently, his research interests involve (i) the chemistry of aliphatic nitro compounds, (ii) the realization of new one-pot protocols for generating and derivatizing heterocyclic systems, (iii) the preparation and use of solid supported reagents, (iv) the development of new sustainable processes, and (v) flow chemical protocols.
Acknowledgments
We wish to express our gratitude to all persons who contributed directly or indirectly to the preparation of this book by their researches and publications. We would like to offer a special thanks to Prof. Dieter Seebach and Prof. Noboru Ono for their historical contributions in this field. Finally, we wish to thank our Camerino’s colleagues for their high helps in many aspects of the chemistry of nitroalkanes.
Roberto Ballini and Alessandro Palmieri
Introduction
Why the choice of a book dedicated to “nitroalkanes”? Usually a generic molecule containing the nitro group is called “nitro compound”; however there are three different typologies of nitro compounds, with distinct chemical behaviors (Figure 1): (i) aromatic nitro compounds, subjected to electrophilic substitution, (ii) conjugated nitroalkenes that, due to the presence of an electrophilic carbon in β-position, are exposed to nucleophilic addition, and (iii) nitroalkanes that, under basic conditions, act as nucleophiles due to the presence of an acidic proton germinal to the nitro group, providing the formation of C—C bond with electrophiles.
Figure 1 Three different typologies of nitro compounds.
Thus, since the studies dedicated to the chemistry of nitroalkanes and their application in organic synthesis are growing year after year in the last two decades, this category of molecules has proven to be one of the most valuable and versatile collection of substances in organic synthesis. Consequently, this book is dedicated exclusively to this class of molecules.
However, as the chemistry of nitroalkanes is constantly expanded, this book should not be considered as “the book” of nitroalkanes but just “the first” (after the pioneering Ono’s book [1]) of a series dedicated to this class of molecules.
Reference
1 1 Ono, N. (2001). The Nitro Group in Organic Synthesis. Wiley-VCH. ISBN 0-471-31611-3.
1 Synthesis of Nitroalkanes
1.1 Synthesis of Nitroalkanes
Simple nitroalkanes (CH3(CH2)0–5NO2, c-C5,6H9–11NO2, i-PrNO2, etc.) are commercially available, while the more complex ones need to be prepared following a variety of synthetic procedure and, in this sense, there are a variety of methods to obtain a large collection of nitroalkanes.
1.1.1 Displacement of Alkyl Halides
Treatment of alkyl halides with metal nitrite is certainly the best known and the most used method for the preparation of nitroalkanes, mainly the primary ones (R1 = H, Scheme 1.1) [1].
Scheme 1.1 Displacement (nitration) of alkyl halides.
In literature a variety of efficient procedures have been reported using sodium or silver nitrite (M = Ag, Victor-Meyer reaction [2]; M = K or Na Kornblum reaction [3]), anyway the formation of nitroalkanes is accomplished by the formation of alkyl nitrite as by-product, removed via distillation or chromatography. The nitrite is formed because of the ambident nature of the nitrite anion, which bears two different nucleophilic centers. The reaction is typically performed at room temperature adding the halide to a stirred mixture of dimethyl formamide (DMF) and metal nitrite. The use of DMF is due to the ability of this solvent to dissolve the nitrite and to accelerate the reaction of the alkali nitrite with the halide, while minimizing any side reaction such as those reported in Scheme 1.1.
An interesting application of the nitration of alkyl halides has been reported [4] for the preparation of fatty nitroalkanes, mainly the polyunsaturated ones, from naturally alcohols (Scheme 1.2) through their successive conversion into (i) bromo alkanes, (ii) iodo alkanes (more reactive vs bromo derivatives), and (iii) nitroalkanes with silver nitrite, in Et2O and at room temperature for three days.
Scheme 1.2 Synthesis of fatty nitroalkanes.
It is important to point out that the need to convert bromo alkanes into the iodo alkanes is due to the fact that, contrary to short-chain bromo alkanes, the longer ones are inert toward the reaction with AgNO2.
Benzylic nitro compounds (aryl nitromethanes) are an important class of nitroalkanes and their preparation shows some drawbacks due to the lack of selectivity, with consequent formation of an amount of nitrite ester. Guillaumet and coworkers [5] reported