Nucleophilic with alcohol nucleophiles

The rather unreactive chlorine of vinyl chloride can be displaced with nucleophiles by the catalytic action of PdCb. The conversion of vinyl chloride to vinyl acetate (797) has been studied extensively from an industrial standpoint[665 671]. DMF is a good solvent. 1,2-Diacetoxyethylene (798) is obtained from dichloroethylene[672]. The exchange reaction suffers steric hindrance. The alkenyl chloride 799 is displaced with an acetoxy group whereas 800 and 801 cannot be displaccd[673,674]. Similarly, exchange reactions of vinyl chloride with alcohols and amines have been carried out[668]. 

Many of the most interesting and useful reactions of aldehydes and ketones involve trans formation of the initial product of nucleophilic addition to some other substance under the reaction conditions An example is the reaction of aldehydes with alcohols under con ditions of acid catalysis The expected product of nucleophilic addition of the alcohol to the carbonyl group is called a hemiacetal The product actually isolated however cor responds to reaction of one mole of the aldehyde with two moles of alcohol to give gem mal diethers known as acetals... 

Reaction with Oxygen Nucleophiles. In the presence of strong acids, eg, H2SO4, HBF, or BF, aziridines react with alcohols to form P-amino ethers (93) ... 

Substitution Reactions on Side Chains. Because the benzyl carbon is the most reactive site on the propanoid side chain, many substitution reactions occur at this position. Typically, substitution reactions occur by attack of a nucleophilic reagent on a benzyl carbon present in the form of a carbonium ion or a methine group in a quinonemethide stmeture. In a reversal of the ether cleavage reactions described, benzyl alcohols and ethers may be transformed to alkyl or aryl ethers by acid-catalyzed etherifications or transetherifications with alcohol or phenol. The conversion of a benzyl alcohol or ether to a sulfonic acid group is among the most important side chain modification reactions because it is essential to the solubilization of lignin in the sulfite pulping process (17). 

Isoxazolium salts can be prepared by reaction with alkyl iodides or sulfates, although the low basicity of isoxazoles and their sensitivity to nucleophilic attack may necessitate special care. Isoxazolium salts containing bulky Af-substituents can be prepared by the reaction of isoxazoles with alcohols in the presence of perchloric acid. For example, the reaction of 3,5-dimethylisoxazole (53) with some alcohols in the presence of 70% perchloric acid gave isoxazolium salts, (54a) in 29%, (54b) in 57% and (54c) in 82% yield 79AHC(25)147, 68JOC2397). Attempts to quaternize 3,5-dimethyl-4-nitroisoxazole failed 71JCS(B)2365). 

Esters react with alcohols in either aeidic or basic solution to exchange alkoxy groups (ester interchange) by mechanisms which parallel hydrolysis. The alcohol or alkoxide acts as the nucleophile ... 

There are alternatives to the addition-elimination mechanism for nucleophilic substitution of acyl chlorides. Certain acyl chlorides are known to react with alcohols by a dissociative mechanism in which acylium ions are intermediates. This mechanism is observed with aroyl halides having electron-releasing substituents. Other acyl halides show reactivity indicative of mixed or borderline mechanisms. The existence of the SnI-like dissociative mechanism reflects the relative stability of acylium ions. 

The addition of nucleophiles to cyclic fluoroolefins has been reviewed by Park et al. [2 ]. The reaction with alcohols proceeds by addition-elimination to yield the cyclic vinylic ether, as illustrated by tlie reaction of l,2-dichloro-3,3-di-fluorocyclopropene Further reaction results in cyclopropane ring opening at the bond opposite the difluoromethylene carbon to give preferentially the methyl and ortho esters of (Z)-3-chloro-2-fluoroacrylic acid and a small amount of dimethyl malonate [29] (equation 8). 

The chloride of triflic acid (trifluoromethanesulfonyl chloride) is an effective sulfonylating agent Like triflic anhydride, it usually reacts with alcohols and other nucleophiles with the formation of the corresponding derivatives of tnflic acid [69] However, in some reactions, it acts as a chlorinating reagent [98] The reactions of tnfluoromethanesulfonyl chloride with 1,3-dicarbonyl compounds or some carboxylic esters in the presence of a base result m the formation of chlonnated products in high yields (equation 49)... 

Other types of leaving groups and of nucleophilic reagents also show greater reactivity at the 4-position 2,4-dichloropyrimidine with alcoholic potassium thiocyanate (to 304) and with chemical monodehalogenation (zinc and ammonia or ammonium chloride), 2,4- lj, 3fi )-pyrimidinedithione with ammonia or... 

In 2,4-disubstituted quinazolines, the 4-position reacts fastest with nucleophiles, generally even when the 4-substituent is a poorer leaving group. 2,4-Dichloroquinazoline undergoes mono-substitution at the 4-position with alcoholic alkoxides (25°, 2 hr, 80-98% yield), phenolic phenoxide (20°, 16 hr, 50% yield), aqueous hydroxide (30°, 3 hr), alcoholic methylmercaptide (20°, exothermically), alkylamines (20°, 10-60 min, 100%... 

We said in Section 19.10 that aldehydes and ketones undergo a rapid and reversible nucleophilic addition reaction with alcohols to form hemiacetals. 

NMR spectroscopy of. 823-824 nucleophilic acyl substitution reactions of, 806-807 reaction with alcohols, 807 reaction with amines, 807... 

Photodriven reactions of Fischer carbenes with alcohols produces esters, the expected product from nucleophilic addition to ketenes. Hydroxycarbene complexes, generated in situ by protonation of the corresponding ate complex, produced a-hydroxyesters in modest yield (Table 15) [103]. Ketals,presumably formed by thermal decomposition of the carbenes, were major by-products. The discovery that amides were readily converted to aminocarbene complexes [104] resulted in an efficient approach to a-amino acids by photodriven reaction of these aminocarbenes with alcohols (Table 16) [105,106]. a-Alkylation of the (methyl)(dibenzylamino)carbene complex followed by photolysis produced a range of racemic alanine derivatives (Eq. 26). With chiral oxazolidine carbene complexes optically active amino acid derivatives were available (Eq. 27). Since both enantiomers of the optically active chromium aminocarbene are equally available, both the natural S and unnatural R amino acid derivatives are equally... 

Sulfonic esters are most frequently prepared by treatment of the corresponding halides with alcohols in the presence of a base. The method is much used for the conversion of alcohols to tosylates, brosylates, and similar sulfonic esters. Both R and R may be alkyl or aryl. The base is often pyridine, which functions as a nucleophilic catalyst, as in the similar alcoholysis of carboxylic acyl halides (10-21). Primary alcohols react the most rapidly, and it is often possible to sulfonate selectively a primary OH group in a molecule that also contains secondary or tertiary OH groups. The reaction with sulfonamides has been much less frequently used and is limited to N,N-disubstituted sulfonamides that is, R" may not be hydrogen. However, within these limits it is a useful reaction. The nucleophile in this case is actually R 0 . However, R" may be hydrogen (as well as alkyl) if the nucleophile is a phenol, so that the product is RS020Ar. Acidic catalysts are used in this case. Sulfonic acids have been converted directly to sulfonates by treatment with triethyl or trimethyl orthoformate HC(OR)3, without catalyst or solvent and with a trialkyl phosphite P(OR)3. ... 

Acyl chlorides are highly reactive acylating agents and react very rapidly with alcohols and other nucleophiles. Preparative procedures often call for use of pyridine as a catalyst. Pyridine catalysis involves initial formation of an acyl pyridinium ion, which then reacts with the alcohol. Pyridine is a better nucleophile than the neutral alcohol, but the acyl pyridinium ion reacts more rapidly with the alcohol than the acyl chloride.103... 

Diazonium salts react with various nucleophiles in water (Eq. 11.62).106 In acidic aqueous solution, p-pheny I e ncbis di azo ni um ion reacts with alcohols more rapidly than it does with water.107 In the presence of nucelophiles such as halides, the substitution products are obtained. Furthermore, diazonium salts of aromatic compounds are excellent substrates for palladium-catalyzed coupling reactions such as the Heck-type reactions in water. 

Imidazolides of aromatic sulfonic acids react much more slowly in alcoholysis reactions than the carboxylic acid imidazolides. Although the reaction with phenols is quantitative when a melt is heated to 100 °C for several hours, with alcohols under these conditions only very slight alcoholysis is observed. In the presence of 0.05 equivalents (catalytic amount) of sodium ethoxide, imidazole sodium, of NaNH2, however, imidazolides of sulfonic acids react with alcohols almost quantitatively and exothermically at room temperature in a very short time to form sulfonic acid esters (sulfonates). (If the ratio of sulfonic acid imidazolide to alcoholate is 1 2, ethers are formed see Chapter 17). The mechanism of catalysis by base corresponds to that operative in the synthesis of carboxylic esters by the imidazolide method. Because of the more pronounced nucleophilic character of alkoxide ions, sulfonates can also be prepared in good yield by alcoholysis of their imidazolides in the presence of hydroxide ions i.e., with alcoholic sodium hydroxide. 45 Examples of syntheses of sulfonates are presented below. 

A mechanism proposed 87) for the alkaline hydrolysis of tetraethyl pyrophosphate, which is markedly accelerated by HPO e ions, has been substantiated by isotopic labeling 88). The nucleophilic attack by HPOJp on the symmetrical pyrophosphate 131 is considered to lead initially to the unsymmetrical P P1-diethyl pyrophosphate dianion 132 which decomposes spontaneously under the conditions of reaction to give the diethyl phosphate anion and POf 102. The latter reacts with water to form inorganic phosphate and with alcohols suclj as methanol and ethylene glycol to produce alkyl phosphates. 

Although halide ions (particularly I and Br ) are strong nucleophiles, they are not strong enough to carry out substitution reactions with alcohols directly. 

A sulfonyl chloride group rapidly reacts with amines in the pH range of 9-10 to form stable sulfonamide bonds. Under these conditions, it also may react with tyrosine —OH groups, aliphatic alcohols, thiols, and histidine side chains. Conjugates of sulfonyl chlorides with sulf-hydryls and imidazole rings are unstable, while esters formed with alcohols are subject to nucleophilic displacement (Nillson and Mosbach, 1984 Scouten and Van der Tweel, 1984). The only stable derivative with proteins therefore is the sulfonamide, formed by reaction with e-lysine... 

As shown in Scheme 199, the 5-aminopyrimidine stmcture may be also incorporated into a more complex bicyclic system. Thus, diazotization of 3-amino-4-oxo-4//-pyrimido[ 1,23 lpyndazincs 1198 followed by treatment with 50% aqueous tetrafluoroboric acid results in precipitation of salts 1199. When heated with alcohols, nucleophilic attack on the carbonyl group opens the pyrimidine ring. The obtained species 1200 assume conformation 1201 that is more suitable for bond formation between the opposite charged nitrogen atoms. Alkyl l-(pyridazin-3-yl)-l//-l,2,3-triazole-4-carboxylates 1202 are obtained in 31-66% yield <2002ARK(viii)143>. 

---