Chloroamination synthesis

The so-called Hofmann-Loeffler-Freytag reaction" " of TV-chloroamines 9 proceeds by a similar mechanism, and is for example used for the synthesis of pyrrolidines 11 ... 

In an effort to more closely mimic the aromatic substitution pattern found in morphine (see A) the pethidine analog containing the m-hydroxy group was prepared as well. Thus, in a synthesis analogous to that used to prepare the parent compound, double alkylation of m-methoxyphenylacetonitrile with the chloroamine. 

The electrophilic amination reaction of organometallic species using mono-, di- and trihaloamines has attracted a lot of attention for the synthesis of amines. Only a few cases have been reported using alkylchloroamines as precursors for the synthesis of tertiary amines One example is the reaction of functionalized aryhnagnesium compounds with benzyl-V-chloroamines 252 providing polyfunctional tertiary amines 253 (equation 164) °. The procedure was also applied for the preparation of chiral V-chloro-amines with retention of chirahty at the a-carbon. However, the amination process is limited to benzyl-V-chloroamines. 

The synthesis of pyrrolidines by the free radical transformation of (V-chloroamines, the Hofmann-Loeffler-Freytag reaction, is of preparative significance. The key step is the formation of a radical cation which abstracts hydrogen intramolecularly to form a carbon-based radical (Scheme 21(a)). This species then abstracts chlorine from another TV-chloroamine (60JA1657, 50JA2118). The observed positional selectivity for hydrogen abstraction is a consequence of the preferred adoption of a six-membered transition state. A typical conversion achieved is indicated in Scheme 21(b). 

The synthesis of pyrrolidines by the free radical transformation of A-chloroamines, the HofmannLoefflerFreytag reaction, is of preparative significance. A typical example is shown in Scheme 33 <1959JOC572>. 

Of the various possible types of -substituted sulfamoyl (sulfamyl) chlorides, the dialkyl compounds are of particular interest because they serve as intermediates in the syntheses of substituted sulfamides (synthesis 28) and of certain of their derivatives (synthesis 29). The dialkyIsul-famoyl chlorides have been prepared by the reaction of sulfuryl chloride with an appropriate amine or its hydrochloride, " by the treatment of secondary 7V-chloroamines with liquid sulfur dioxide, and by the reaction of dialkyl-aminosulfinic acids with chlorine in carbon tetrachloride. Although either of the first two procedures can be recommended in terms of convenience and yield, the availability of starting materials normally dictates that the first be used. It is of interest that treatment of sulfuryl chloride with either ammonia or ammonium chloride in terms of this procedure does not give the parent sulfamoyl chloride, H2NSO2CI. This compound is obtained in an altogether different way. ... 

Tlie intramolecular 1,4-chloroamination of 89 was applied to the synthesis of the amaryllidaceae alkaloids a- and y-lycorane (Scheme 8-34) [114]. The hexahydroindole 90... 

The Sharpless regioreversed asymmetric aminohydroxylation protocol was used as a key step in the total synthesis of ustiloxin D by M.M. Joullie and co-workers.The ( )-ethyl cinnamate derivative was subjected to in situ generated sodium salt of the N-Cbz chloroamine in the presence of catalytic amounts of the anthraquinone-based chiral ligand to afford the desired A/-Cbz protected (2S,3R)-(3-hydroxy amino ester in good yield and with good diastereoselectivity. 

Aziridine synthesis. Gloss and Brois devised a new synthesis in which a tetra-alkylethylene is converted into the blue monomeric chloronitroso derivative this is reduced with stannous chloride in hydrochloric acid, and the chloroamine without... 

This type of transformation has been employed for the synthesis of several different nitrogen heterocycles [98], and an analogous reaction of unsaturated A-chloroamines that generates pyrrolidine products has also been described [99]. 

In the short synthesis of (-)-524 by Back and Nakajima, an efficient cyclization between the proline-derived chloroamine 556 and the alkynylsulfone 557 yielded the unsaturated indolizidine 558 (94%) (Scheme 71) (451). Stereoselective reduction of the conjugated double bond with sodium cyanoborohydride followed by cleavage of the sulfone with sodium in ammonia yielded a mixture of (-)-524 and the unsaturated analog 559. Catalytic hydrogenation ensured complete conversion of 559 into (- )-indolizidine 167B (524). 

Michael addition of acrylic acid to the chloroamine 32 is straightforward and Friedel-Crafts cyclisation of 35 gives only 31, presumably because the position next to the chlorine atom is slightly disfavoured both sterically and electronically. Chlorination and oxidation are conveniently carried out in the same step and the two halves (26 and 28) of this convergent synthesis are combined to give amopyroquine 25. 

Another synthesis of a quaternary salt (8) was developed by Meyer and Sapianchiay for the purpose of studying the steric course of formation of the pyrrolizidine system.9 Photolysis of the N-chloroamine (9) in a Hofmann-Loeffler-Freytag reaction [Eq. (4)], gave an intermediate that yielded the pyrrolizidine salt (8) in an intramolecular N-alkylation. The product was the cis-isomer, reflecting the greater degree of strain in the trans-fusion of two five-membered rings. 

As we were not only interested in the development of a racemization method but also wanted to evaluate an asymmetric synthesis articulated around the imine intermediate 7 vide infra), we initially investigated its controlled preparation by oxidation of the unwanted (7 )-TH[3C 4 obtained from the mother liquors. Among the various methods initially tested, good results (approximately 75 to 80% in situ yield of imine 7) were obtained with NaOCl in methanol/THF at 0 to 5°C for 3 h. The major by-product is the overoxidized (3-carboline derivative (5 to 10%), although in some experiments, low levels of the unstable N-chloroamine intermediate were also detected. Later on, approximately 68% in situ yield was obtained with tetra-n-propylammonium perruthenate (0.05 equiv) as catalyst with iV-methylmorpholine oxide (1.5 equiv) as cooxidant in acetonitrile at room temperature. However, in this latter method, up to 16% of totally oxidized (3-carboline was also formed. The imine 7 was then directly reduced with sodium borohydride to produce the racemic material in approximately 50% isolated overall yield. Although the aromatic (3-carboline by-product was easily removed upon salt formation, the above approach suffered from several major drawbacks difficulty to control the overoxidation of the desired dihydro-(3-carboline to the (3-carboline on... 

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