1-chloro-1-nitroso cyclohexane

Kresze and cowoikers have used nitroso Diels-Alder reactions in synthesis of a variety of inosamines and related compounds. One example of this work is the synthesis of conduramine-Fl (92) as shown in equation (34). In this case, diene (91) reacted with a-chloro nitroso cyclohexane to afford adduct (91) as the only product. Just why this stereoisomer was formed is not obvious. Compound (91) could be converted to the conduramine in a few steps. 

Since the question of the necessary conditions for isomerization of nitroso-cyclohexane to cyclohexanone oxime is of considerable commercial importance, it has been shown that this tautomerization is favored by the presence of gaseous hydrogen chloride, particularly at a wavelength of 300 mp. [57]. When cyclohexane is saturated with hydrogen chloride, treated with nitric oxide, and exposed to a source of ultraviolet radiation, the oxime forms along with a trace of 1-chloro-l-nitrosocyclohexane [58]. Cyclooctane seems to form the corresponding oxime and the chloronitroso compound, but under no circumstances nitrosocyclooctane [58]. 

In carbon tetrachloride at —30°C the product mixture consisted of 95% of trans-1 -chloro-2-nitrosocyclohexane dimer and 5% of trans-1 -nitro-2-nitroso-cyclohexane dimer. In trichloroethylene at —30°C, a 50-50 mixture of these two products was formed [15]. 

In a series of papers24a c, Oppolzer et al. introduced another procedure for the enantioselec-tive amination of enolates based on the A-acyl camphor sultam 1 as a chiral template and 1-chloro-l-nitroso cyclohexane (2) as electrophile. 

Replacing the nitrosyl chloride by a mixture of nitric oxide and chlorine has also proved successful in the nitrosation of irradiated saturated hydrocarbons. According to the conditions and the proportions in which the oxide and chlorine are used, cyclohexane affords as main product 1-chloro-l-nitroso-cyclohexane, dimeric nitrosocyclohexane, or cyclohexanone oxime. Experimental details of this interesting reaction, which has industrial interest, will be found in a review by Muller et ah212 and the papers cited therein. 

Oppolzer s camphor-based sultams 92 proved itself as an efficient, robust auxiliary for enolate amination with 1-chloro-l-nitroso cyclohexane 486 as an electrophile. Thus, sultams 92 were first deprotonated with NaHMDS, and to the sodium enolates thus formed was added a solution of the blue nitrosochloride 486. Decolorization occurred immediately, and the mixture was quenched with hydrochloric acid to give hydroxylamines 487, in all cases as essentially pure diastereomers. The reductive cleavage of the nitrogen-oxygen bond was achieved with zinc dust to yield a-aminoacyl sultams 488. By mild hydrolysis with lithium hydroxide, the chiral auxiliary 91 was removed and recovered under concomitant formation of a-amino acids 490. Any racemization was avoided by applying this procedure, even in the case of the labile substrates with R equals a phenyl or / r -methoxyphenyl substituent. On the other hand, the auxiliary could be cleaved at the stage of hydroxylamines 487, so that not only a-amino acids 490 but also a-hydroxyamino acids 489 became available with excellent enantiomeric purity (Scheme 4.103) [232]. 

Spectrophotometric methods based on ion associates with basic dyes are very sensitive. The Co-thiocyanate complex was associated with Malachite Green (CCI4 -i- cyclohexane), (e = 8.6-10 ) [61], Turquoise Blue (triphenylmethane dye) (toluene -1- DMF) [62], and 6-nitrodimethyline-carbocyanine [63,64]. The anionic complex of Co with chloro-oxine [65] associated with Rhodamine 6G was extracted with benzene. The complex of Co with 2-nitroso-l-hydroxynaphthalene-4-sulphonic acid was extracted into CHCI3 as the associate with a basic azo dye (e = 1.66-10 at 566 nm) [66]. 

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