Sulfonic acid esters synthesis with addition

Many reports have focused on the functionalization and derivatization of cyclo-pentadienyl groups bound to iron in ferrocene complexes. As an example, a series of ferrocenyl esters have been prepared via solvent-free reactions of ferrocenoyl fluoride with substituted phenols after microwave heating for just 1 min. " In the case of 4-bromophenol, the YIF was 1.2, but most substrates gave somewhat lower yields than the conventional method. However, the microwave approach did not require the addition of A, A -dimethylaminopyridine that was necessary conventionally. Other reports include a green approach to the acylation of ferrocene using the polymeric sulfonic acid Nation as an acid catalyst " and a one-pot approach to the synthesis of l,5-dioxo-3-substituted[5]ferrocenophanes from l,T-diacetylferrocene and aldehydes via a Claisen-Schmidt reaction. " " ... 

Nitroalkenes react with lithium dianions of carboxylic acids or with hthium enolates at -100 °C, and subsequent treatment of the Michael adducts with aqueous acid gives y-keto acids or esters in a one-pot operation, respectively (Eq. 4.52).66 The sequence of Michael addition to nitroalkenes and Nef reaction (Section 6.1) provides a useful tool for organic synthesis. For example, the addition of carbanions derived from sulfones to nitroalkenes followed by the Nef reaction and elimination of the sulfonyl group gives a,P-unsaturated ketones (Eq. 4.53).67... 

Addition of sulfides and sulfones to acid derivatives has been investigated by Agawa. Phenyl and methyl (trimethylsilyl)methyl sulfides and sulfones added to amides (323) to produce the aminovinyl sulfides (324 equation 74) and sulfone (326 equation 7S). The reactions proceeded in good yield with some examples of stereocontrolled synthesis of the ( )-isomer. Other acid derivatives such as esters, carbonates and ureas were investigated, but gave inconsistent results. 

In the synthesis of hydroxamic acid 19a, having a free quaternary amino group (see Scheme 4.4), the intermediate sulfone 21 was synthesized by Pd-catalyzed reaction of phenol with p-bromo derivative 20 [24], Lithiation of 20, followed by nucleophilic addition to the A-Cbz imine of trifluoropyruvate 22 [25] afforded the a-CF3 a-amino acid derivative 23 in fair yields. Basic hydrolysis of the ester function gave the carboxylic acid 24, which was submitted to condensation with ()-15 n-hydroxylamine, affording hydroxamate 25. The subsequent hydrogenolysis of 25 afforded the target molecule 19a. 

The conjugate base of an alkyne is an alkyne anion (older literature refers to them as acetylides), and it is generated by reaction with a strong base and is a carbanion. It funetions as a nucleophile (a source of nucleophilic carbon) in Sn2 reactions with halides and sulfonate esters. Acetylides react with ketones, with aldehydes via nucleophilic acyl addition and with acid derivatives via nucleophilic acyl substitution. Acetylides are, therefore, important carbanion synthons for the creation of new carbon-carbon bonds. Some of the chemistry presented in this section will deal with the synthesis of alkynes and properly belongs in Chapter 2. It is presented here, however, to give some continuity to the discussion of acetylides. 

These amidines have been extensively applied to dehydrohalogenation in organic synthesis and in some cases DBU (1) is more effective than DBN (2) [5]. A double bond can be also introduced into organic molecules by elimination of sulfonate ester instead of the halogen atom (i.e. dehydrosulfonation in addition to dehydrohalogenation). Furthermore, these amidines can be applied to the Wittig reaction [6], aldol condensation [6], 1,3-allyl rearrangement [7] and epimerization of the (3-lactam skeleton (at Ce of the penicillic acid derivatives). Sterically hindered phenols (e.g. 2,6-di(ferf-butyl)-4-fluorophenol) are (9-acetylated with DBU (1), which is superior to sodium hydroxide in the synthesis [8]. 

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