Esters chlorosulfite

When the reaction is performed in dioxane solution, an o onium ion is formed from the solvent and the chlorosulfite ester. The oxonium ion then undergoes substitution by chloride. l vo inversioRs are involved so that tiie result is overall retention. ... 

Another general method for converting alcohols to halides involves reactions with halides of certain nonmetallic elements. Thionyl chloride, phosphorus trichloride, and phosphorus tribromide are the most common examples of this group of reagents. These reagents are suitable for alcohols that are neither acid sensitive nor prone to structural rearrangement. The reaction of alcohols with thionyl chloride initially results in the formation of a chlorosulfite ester. There are two mechanisms by which the chlorosulfite can be converted to a chloride. In aprotic nucleophilic solvents, such as dioxane, solvent participation can lead to overall retention of configuration.7... 

In the absence of solvent participation, chloride attack on the chlorosulfite ester leads to product with inversion of configuration. 

Problom 7.62 Depending on the solvent, ROH reacts with SOCl to give RCl by two pathways, each of which involves formation of a chlorosulfite ester. 

The reaction of the chlorosulfite ester Xld with palladium(O) may take place by direct nucleophilic displacement of the chlorosulfite group at carbon by palladium or via an intermediate sulfite complex Xlld. The direct nucleophilic displacement would be expected to take place with inversion of configuration. The reaction of the chlorosulfite ester to afford... 

The first step is an allylic chloride displacement on a chlorosulfite ester generated from the tertiary vinyl carbinol and thionyl chloride. Attack of chloride on an allylic carbocation intermediate can equally well be envisaged. The subsequent conversion is simply an S 2 displacement by acetate ion (Scheme 10.6). 

The reaction of 25 with thionyl chloride almost certainly leads to the chlorosulfite ester 32 (Scheme 11.11). An internal nucleophilic displacement then occurs by the adjacent benzyloxycarbonyl group to form the... 

Under the proper conditions, thionyl chloride reacts by the interesting mechanism summarized next. In the first step, the nonbonding electrons of the hydroxyl oxygen atom attack the electrophilic sulfur atom of thionyl chloride. A chloride ion is expelled, and a proton is lost to give a chlorosulfite ester. In the next step, the chlorosulfite ester ionizes (when R = 2° or 3°), and the sulfur atom quickly delivers chloride to the... 

In order to get better stereochemical control and to circumvent the use of sulfinyl chlorides in the synthesis of sulfinate esters, the reaction of chlorosulfite esters of... 

The chlorosulfite method, which is claimed to be indicated for the synthesis of alkanesulfmates, works only in the case of methanesulfinate. The levels of control of diastereomeric excess with arylzinc and any arylmetal were in general very low. Additionally, reaction of chlorosulfite esters with alcohols and amines produced sulfinic acid derivatives in good yield but with low selectivity (< 2 1). 

Step 1 The hydroxyl group oxygen attacks sulfur and displaces chloride to give a protonated chlorosulfite ester ... 

The Sni mechanism (substitution-nucleophilic-internal), as originally proposed, postulated a front-side displacement occurring via a four-center transition state. It is now clearly established that such a process has never been observed, and that all the reactions proposed to proceed by SnI mechanisms involve ion pairs. The Sni mechanism was initially suggested to explain the observed stereochemistry of chlorosulfite decomposition. Chlorosulfite esters are formed by reaction of alcohols with thionyl chloride, and are the key reactive intermediates in the conversion of alcohols to chlorides with thionyl chloride. Nucleophilic attack by the chloride of the chlorosulfite ester was considered to be concerted with cleavage of the C-O bond ... 

The conversion of alcohols to alkyl chlorides using thionyl chloride was described previously in this chapter, in Section 5.8. It was pointed out that the stereochemistry of the reaction is sensitive to the precise experimental conditions employed, and can vary from inversion of configuration to retention of configuration, depending on the circumstances attending decomposition of the intermediate chlorosulfite ester. 

A few nucleophilic substitution reactions have been observed to proceed with a high degree of retention of configuration. One example is reaction of alcohols with thionyl chloride, which under some conditions gives predominantly product of retained configuration. This reaction is believed to involve formation of a chlorosulfite ester. This can then react with chloride to give inverted product. 

Since alkyl halides are extremely useful in synthesis, it is not surprising that chemists have devised several ways to prepare them from alcohols. For example, thionyl chloride (eq. 7.31) reacts with alcohols to give alkyl chlorides. The alcohol is first converted to a chlorosulfite ester intermediate, a step that converts the hydroxyl group into a good leaving group. This is followed by a nucleophilic substitution whose mechanism (Sj l or 5 2) depends on whether the alcohol is primary, secondary, or tertiary. 

The initial product in this reaction is a chlorosulfite ester. Mechanisms of breakdown of the intermediate chlorosulfite ester involve both Sn2 displacement by chloride ion to give the alkyl chloride, sulfur dioxide (SO2), and a chloride ion (Fig. 7.43a), as well as direct decomposition to SO2 and a pair of ions that recombine (Fig. 7.43b). 

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