Interconversion of functional groups

There are many transition metal ion oxidants used in organic chemistry for the interconversion of functional groups. Those which have been used for the preparation of sulphones from sulphoxides will be discussed below. It is very interesting to note that this type of oxidant often reacts more rapidly with sulphoxides than with sulphides and so sulphoxides may be selectively oxidized with transition metal ion oxidants in the presence of sulphides. This is in direct contrast to the oxidation of sulphides and sulphoxides with peracids and periodate, for example, where the rate of reaction of the sulphide is more than 100 times that for the corresponding sulphoxide. 

Chapters 1 and 2 dealt with formation of new carbon-carbon bonds by reactions in which one carbon acts as the nucleophile and another as the electrophile. In this chapter we turn our attention to noncarbon nucleophiles. Nucleophilic substitution is used in a variety of interconversions of functional groups. We discuss substitution at both sp3 carbon and carbonyl groups. Substitution at saturated carbon usually involves the Sjv2 mechanism, whereas substitution at carbonyl groups usually occurs by addition-elimination. 

Only transformations in the longest linear sequence (LLS) are considered. The term skeleton constructions refers to C-C and C-O bond formations (notwithstanding redox reactions) that directly introduce native structural features of the bryostatins without further modification. The term other functional group manipulations refers to steps that indirectly introduce native structural elements, the interconversion of functional groups (e.g., the introduction and removal of auxiliaries) and miscellaneous transformations that do not involve skeleton construction... 

The major portion of most texts on organic chemistry focuses upon reactions that result in the interconversion of functional groups. This huge body of factual material s will not be reviewed here in detail as it is impossible within the volume of this book and unnecessary for our purposes. Our goal is to highlight the importance of these interconversions in a total synthesis. The immense diversity of transformations can be actually reduced to a few types that we hope are sufficient to provide the reader with an understanding of the principles necessary to select the conversions for a chosen synthetic plan. 

In view of myriad of options available for the interconversions of functional groups at oxidation level 1, one can safely consider all of these functions to be synthetically equivalent. In essence, this means that if it is necessary to introduce a certain functional group into a given structure, the task can be considered achievable if a constructive reaction chosen to create the C-C bond leads to the formation of a double bond or hydroxyl group at the desired location. 

Until now, we have portrayed functional group transformations as secondary tools, somehow associated with the more important task of creating a carbon skeleton. There does exist, however, a wide class of tasks in which the interconversions of functional groups constitute the very essence of a synthetic problem. 

Because a large number of functional group transformations are affected by the reactions covered in the book, we felt that tables showing the interconversion of functional groups should be included. 

In this section syntheses producing the ring systems will be described interconversion of functional groups will be found in Section III. 

By the silation of acidic hydrogens of conventional synthetic reagents affords various organosilicon compounds, which are employed for interconversion of functional groups. In certain reactions, diazomethane can be substituted for trimethylsilyldia-zomethane which is thermally stable and can be handled safely (eq (35)) [32]. 

Decide which reaction(s) are needed to achieve the interconversion of functional groups. Before applying any reaction to the targeted functional group, determine whether any other functional groups in the compound will react with the reagents proposed. If these other reactions are undesirable, determine whether the functional groups can be protected. 

A summary of reactions from this chapter that enable the interconversion of functional groups. 

Alkoxysilane silanol condensation reactions play an important role in sol-gel technology, the manufacture of silicone resins, the vulcanization of silicones and in surface modiflcation by alkoxysilanes. There have been recent investigations by Chojnowski and coworkers into the kinetics of acid-catalysed heterofunctional condensation of model alkoxy and silanol functional siloxanes. The heterofunctional reaction involving SiOEt and SiOH competes with the homofunctional reaction of SiOH with SiOH. The rates of each process are similar, but are influenced by the medium and hence by the concentration of the reactants. Hydrolysis of the ethoxysiloxane as well as ethanolysis of the silanol groups leads to extensive interconversion of functional groups. These interconversion processes are two orders of magnitude faster than those of the condensation reactions. 

In the second group we consider interconversions of functional groups with the exchange of hetereoatoms, breaking of old and formation of new C-heteroatom bonds. Examples of these transformations are interconversion of an amide to ester, thioketone to ketone or alkylhalide to alcohol. They are related to S5mthetic reactions formation of amide from ester, thioketone from ketone or haloalkane from alcohol. Characteristic of all the above interconversions is the disconnection (imaginative process ) of the C-heteroatom bond, C-N or C-O. In the synthetic direction C-N, C-S and C-Hal bonds are formed. Therefore, such FGIs are also denoted as DIS-C-X, where X stands for heteroatom. 

In the former examples we applied afunctional group addition to create target molecules that are more convenient for disconnection. This concept and other interconversions of functional groups are practiced in the examples that follow. 

Several examples of organic synthesis given with examples of webs showing interconversions of functional groups. 

Interconversion of Functional Groups. The reaction of Me2BBr with MEM and MOM ethers is believed to proceed via a-bromo ether intermediates. It is possible to trap these intermediates with nucleophiles such as thiols, alcohols, and cyanide. An example of the utility of this sequence is the conversion of a readily prepared MOM ether into an MTM ether (eq 10). ... 

---