Alkyl halides heteroatom-substituted

Strong nucleophiles such as organolithium or organomagnesium derivatives do not react with substituted or unsubstituted phosphabenzene or arsabenzene (39, Y = P or As) by nucleophilic substitution as in the case of pyridines, but by addition to the heteroatom forming intermediate anions 40. These can then be converted into nonaromatic compounds by reaction with water to yield 1-alkyl-1,2-dihydro-derivatives 41, or they can be alkylated by an alkyl halide with the same or a different alkyl group, when two products may result a 1,2-dialkyl-1,2-dihydro 40-derivative 42, or a -derivative 43. The former products are kinetically controlled, whereas the latter compounds are thermodynamically controlled, so that one may favor the desired product by choosing the appropriate reaction conditions. 

The corresponding reactions are mostly ionic involving nucleophilic displacement by SnI, Sn2 or carbonyl substitution with amines, alcohols and thiols on carbon electrophiles. The normal polarity of the disconnection 1 will be a cationic carbon synthon 2 and an anionic heteroatom synthon 3 represented by acyl or alkyl halides 4 as electrophiles and amines, alcohol or thiols 5 as nucleophiles. 

Another type of substitution reaction is increasing in popularity—the use of an allylic substrate, such as an allyl acetate where the nucleophile is introduced with stereochemical control in the presence of a palladium catalyst and a chiral ligand. Reactions where a chiral anion, be it derived from a chiral heteroatom group, such as a sulfoxide, or an auxiliary, such as Evans s oxazolidinones, are not included in this chapter because the alkyl halide is usually relatively simple and the stereochemical selectivity is derived from the system itself. 

Now, let us take a simple functional group such as an OH and substitute it on our carbon atom. The carbinol we now have is capable of yielding only one C-C bond by way of substitution or one unsaturation on our carbon by means of elimination. Alcohols should then be classified under the FN = 1 group. Other oxygen based substituents such as ethers, carboxylic and sulfonic esters, and other heteroatom-containing derivatives such as amines and sulfides behave similarly, as long as we have only one of the heteroatoms substituted on our central carbon. By the same token, alkyl halides, diazonium salts, and even the carbenium ion itself are all capable of giving only one C-C bond with carbon... 

Amines caimot undergo the substitution and elimination reactions that alkyl halides undergo, because the leaving groups of amines are too basic. Protonated amines also cannot undergo the reactions that protonated alcohols and protonated ethers undergo. Amines are easily oxidized. Saturated heterocycles containing five or more atoms have physical and chemical properties typical of acyclic compounds that contain the same heteroatom. 

Neutral cr-alkyliron complexes are obtained upon reaction of Na[Cp(C0)2pe] (5) with alkyl halides (9) (Scheme 6), and as with Collman s reagent this occurs in an Sn2 fashion with inversion of configuration at the carbon atom. Epoxides also participate in this reaction, but tertiary alkyl halides are poor substrates. Alternatively, complexes (9) may be prepared by reaction of an appropriate metal alkyl with Cp(C0)2peX (6). Typically complexes of this type are prepared in order to gain access to the synthetically useful cationic rf--alkene iron complexes (Section 4.1.2). Also, nucleophilic addition of (5) to heteroatom-substituted alkyl halides (such as methoxymethylchloride or chloromethyl methyl sulfide) affords complexes of type (9) that can be converted to cationic... 

Nucleophilic Substitution on Alkyl Halides by Heteroatoms. A number of more or less activated alkyl halides, such as benzyl halides and allyl halides, undergo substitution reactions mediated by AgBp4 in the presence of a heteroatom nucleophile. For example, treatment of pentamethylcyclopentadienyl bromide with AgBp4 in the presence of a nucleophile gives the corresponding substituted product (eq 2). Thiols, amines, and alcohols have been used as nucleophiles. ... 

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