1,2-addition sulfone-containing nucleophiles

The 1,2-addition of sulfone-containing nucleophiles to aldehydes is a highly valuable tool in synthetic chemistry. H owever, since the first addition of a-chlorophenyl-sulfone to aromatic aldehydes under PTC in 1998 [65], only one further approach has been reported. Hu et al. reported the enantioselective 1,2-addition of Me3SiCp2 S02Ph and PhS02Cp2H to aromatic aldehydes catalyzed by a chiral aUcaloid-based quaternary ammonium salt (Scheme 29.30) [66], Several chiral ammonium salts were screened and the best results were obtained with cinchonine and quinine... 

Addition of a nucleophile to the C-6 position of cytosine often results in fascile displacement reactions occurring at the N4 location. With hydroxylamine attack, nucleophilic displacement causes the formation of an N4-hydroxy derivative. A particularly important reaction for bioconjugate chemistry, however, is that of nucleophilic bisulfite addition to the C-6 position. Sulfonation of cytosine can lead to two distinct reaction products. At acid pH wherein the N-3 nitrogen is protonated, bisulfite reaction results in the 6-sulfonate product followed by spontaneous hydrolysis. Raising the pH to alkaline conditions causes effective formation of uracil. If bisulfite addition is done in the presence of a nucleophile, such as a primary amine or hydrazide compound, then transamination at the N4 position can take place instead of hydrolysis (Fig. 38). This is an important mechanism for adding spacer arm functionalities and other small molecules to cytosine-containing oligonucleotides (see Chapter 17, Section 2.1). 

Sulfonation of 2-hydroxy-nicotinic acid 191 with sulfuric acid does not work but 30% oleum, that is sulfuric acid containing a 30% excess of S03, gives a 90% yield of 190. This might easily occur by iV-sulfonation 192, addition of some nucleophile 193, [1,5] shift 194 and elimination. Note that the position between C02H and N in 192 is blocked by the OH group so addition must occur on the other side in contrast to 184. This compound will also be discussed in chapter 33. 

Fiber-Reactive Dyes. These dyes can enter iato chemical reaction with the fiber and form a covalent bond to become an iategral part of the fiber polymer. They therefore have exceptional wetfastness. Thein main use is on ceUulosic fibers where they are appHed neutral and then chemical reaction is initiated by the addition of alkaH. Reaction with the ceUulose can be by either nucleophilic substitution, using, for example, dyes containing activated halogen substituents, or by addition to the double bond in, for example, vinyl sulfone, —S02CH=CH2, groups. 

Electron transfer was mediated by metallic silver colloids whose surfaces contained either a strong (SH ) or a weak (CN ) nucleophile [531]. The former case is illustrated by changes in the absorption spectrum of a 1.0 x 10 4 M, deaerated solution of metallic silver particles, subsequent to the consecutive addition of 2.0 x 10 4 M NaSH and 3.0 x 10-4 M anthracene quinone sulfonic acid, AQS (Fig. 85) [506]. The origin of the intensity decrease and the broadening of the silver plasmon absorption band upon the addition of nucleophilic SH is incompletely understood. However, that an absorption... 

In addition to sulfone, phenyl units, and ether moieties, the main backbone of polysulfones can contain a number of other connecting units. The most notable such connecting group is the isopropylidene linkage which is part of the repeat unit of the well-known bisphenol A-based polysulfone. It is difficult to clearly describe the chemical makeup of polysulfones without reference to the chemistry used to synthesize them. There are several routes for the synthesis of polysulfones, but the one which has proved to be most practical and versatile over the years is by aromatic nucleophilic substitution. This polycondensation route is based on reaction of essentially equimolar quantities of 4,4,-dihalodiphenylsulfone (usually dichlorodiphenylsulfone (DCDPS)) with a bisphenol in the presence of base thereby forming the aromatic ether bonds and eliminating an alkali salt as a by-product. This route is employed almost exclusively for the manufacture of polysulfones on a commercial scale. 

Isotellurazoles 4 were obtained in low yields (3-11%) by the one-pot reaction of alkynyl ketones with hydroxylamino-O-sulfonic acid and K2Te in aqueous solution containing sodium acetate (83S824 87H1587). A plausible mechanism of the reaction includes formation of the oxime derivative and subsequent nucleophilic addition of telluride anion to the triple bond followed by cyclization to 4. The reaction is accompanied by the formation of telluro bis(alkenyl ketones) 5 in yields approximately equal to those of 4. When alkynyl aldehydes are used instead of ketones, the single reaction products are the tellurobis(alkenyl nitriles) 6 (83S824). 

Simple sulfonyl carbanions which do not contain additional carbanion-stabilising groups, e.g. carbonyl groups or heteroatoms, can be readily alkylated in high yield by modern techniques with the use of alkyllithiums and lithium amide bases. A number of allylic halides have been successfully used. In allylic halides, the halogen directly attached to the double-bonded carbon is relatively inert towards nucleophilic attack (Scheme 41). In this way, sulfones (96) can be transformed via desulfonation into vinyl halides (97) or into ketones (98) by hydrolysis (Scheme 41). In contrast to ordinary alkyl sulfones, triflones (99) can be alkylated under mildly basic conditions (potassium carbonate in boiling acetonitrile) (Scheme 42). The ease of carbanion formation from triflones (99) arises from the additional electron-withdrawing (-1) effect of the trifluoromethyl moiety. 

In most cases, treatment of allylic halides containing one ASG with a nucleophile does not result in formation of electrophilic cyclopropanes (MIRC product) instead, other reaction pathways are followed, e.g. addition, substitution, rearrangement and elimination reactions.However, with certain alkenes or nucleophiles or under the appropriate conditions a conjugate addition-nucleophilic substitution pathway is favored, resulting in cyclopropanes substituted with one ASG. Representative examples are compiled in Tables 20 and 21 where organometallic compounds or active methylene compounds are used as the nucleophilic species in combination with allyl bromides containing an ester or a sulfone as ASG. 

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