A-Chloronitroso compound

Hypochlorous acid adds to oximes of cyclic ketones forming intermediate a-chloronitroso compounds that can be converted to nitro compounds (108). 

Dimethylsulfonium phenacylide (574) underwent C-alkylation with a-chloronitroso compounds such as (575). The intermediate (576) immediately cyclized to the isoxazoline (577). With a more basic ylide such as dimethylsulfonium methoxycarbonylmethylide the initial alkylation product underwent elimination of the sulfonium group to an alkene rather than its displacement (72T3845). 

Optically active dihydrooxazines 230 are produced by the reaction of the chiral a-chloronitroso compound 228 derived from D-mannofuranose with a variety of 1,3-dienes in the presence of ethanol at low temperatures via the primary adducts 229 (equation 122). Penta-1,3-diene, for instance, yields a mixture of the regioisomers 231 and 232113. 

Dimethylsulfonium phenacylide (67) undergoes C-alkylation with a-chloronitroso compounds (66) intermediates (68) cyclize to the isoxazolines (69) (72T3845). 

Boer and co-workers examined the reaction of sterically hindered a-chloronitroso compounds with Me3Al [111]. The conspicuous reaction sequence is interpreted in terms of initial ring rupture, methane evolution and chlorine migration from carbon to aluminum intramolecular reaction of the carbon-carbon double bond with the rather electrophilic carbon atom from the nitrile oxide moiety leads to a seven-mem-bered ring with an exocyclic double bond as shown in Sch. 75. After hydrolysis, the corresponding oxime is obtained. 

Nitroso compounds of various structural types have been widely utilized as Diels-Alder dienophiles, and the subject has been comprehensively reviewed several times (77CSR1 82T3087). It has been known for many years that a-chloronitroso compounds react with 1,3-dienes to yield unstable adducts of... 

Besides scission of the /3-carbon-hydrogen bond, scission of the /3-carbon-halogen bond is also possible. In photolyses of a-chloronitroso compound 188 nitrone 190 is obtained177. Its formation is discussed via an intermediate aminyloxide 189 which, however, has not been detected by ESR spectroscopy. For the formation of chloro-... 

Alternate routes to chiral a-amino acids and a-amino alcohols that apparently proceed with somewhat higher diasteroselectivity involve the reactions of achiral a-chloronitroso compounds with chiral enolates or of chiral a-chloronitroso compounds with achiral enolates (see section on the animation with nitroso compounds in Comparison with Other Methods), but they have not been applied nearly as frequently as the animations described above. 

Leonard et al. have used the major adduct from isoprene cycloaddition to a chloronitroso compound in an efficient total synthesis of the cell division stimulant c/j-zeatin [Eq. (13)]. ... 

For example, addition of a chloronitroso compound to 1,3-cyclohex-adiene [Eq. (12)]21... 

The regiochemistry of the addition of a-chloronitroso compounds with unsymmetrical acyclic dienes has been probed, and some results are listed in Table 3-II.lb 3a 23 In general, orientational preferences are in accord with those observed for arylnitroso compounds (cf. Table 3-1). As noted above, a glaring exception is the case of isoprene, which gives the opposite selectivities with chloronitroso compounds and nitrosobenzene. It was suggested that steric factors become important in cycloadditions... 

Kresze and co-workers have looked at the possibility of effecting nitroso Diels-Alder reactions enantioselectively. In a preliminary experiment, the optically active a-chloronitroso compound in Eq. (15)... 

Sterically unhindered and certain moderately hindered a-chloronitroso compounds (142) react with trimethylaluminium to give the methyl nitrones (143) (Scheme 228).Relatively hindered a-chloronitroso compounds such as (144) can undergo fragmentation followed by ring closure, in an overall sequence which leads to a ring expansion (Scheme 228). 516... 

Several aliphatic nitroso compounds are known to act as hetero-dienophiles, but only the a-halonitroso type has been used to any significant extent. It has been known for about 40 years - that these a-chloronitroso compounds react readily with 1,3-dienes to yield unstable adducts [Eq. (11)]. 

Another type of nitroso dienophile that has found use in organic synthesis bears an a-chloro substituent. Such a-chloronitroso compounds react with dienes to give the usual dihydro-oxazine product, however, in the presence of an alcoholic solvent, this cycloadduct reacts further and the product actually isolated is the A-unsubstituted dihydro-oxazine (3.32). Hence the use of a-chloronitroso dienophiles gives the product formed, in effect, by addition of HN=0 to the diene. This has been exploited by a number of research groups, an example of which, towards the natural compound conduramine FI, is illustrated in Scheme 3.33. 

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