Pseudohalogens, addition

Iodine isocyanate was used to synthesize the first steroidal aziridine, 2, 3 -iminocholestane (95). from 5a-cholest-2-ene (91). This reaction sequence which is believed to proceed through a three-membered ring iodonium ion (92) illustrates the limitation of pseudohalogen additions for the synthesis of -aziridines. The iodonium complex forms from the least hindered side (usually alpha) and is opened tmK5-diaxially to give a -oriented nitrogen function. The 3a-iodo-2 -isocyanate (93) is converted by treatment with... 

Pseudohalogen addition reactions reported recently include those of iodine azide (IN3), which readily attacks olefinic steroids (e.g. 139) to give iodo-azides... 

Addition of halogens and pseudohalogens to the cyclopropylthiocarbene chromium complexes 122 affords the 1,4-dihalo-1-phenylthio-l-alkenes 123 stereoselectively [65]. Electrophilic halogen is likely to activate the carbene complexes, followed by the homo-Michael addition of halide anion. (Scheme 44)... 

Bis [(trifluoromethyl)thio] acetaldehyde (83a) has been prepared from an enam-ine precursor (84), although refluxing in aqueous ethanolic HCl is required to effect this reaction.The aldehyde is less stable than its enol tautomer (83b), and many reactions typical of aldehydes fail. For example, addition of aqueous silver nitrate immediately yields the silver salt of (83b), rather than giving precipitation of (elemental) silver. The (trifluoromethyl)thio substituent has pseudohalogenic character and, together with the hydroxy group, stabilizes the alkene tautomer in the manner of a push-pull alkene. The enol-aldehyde equilibrium mixture in acetonitrile shows an apparent of 2.6 when titrated with aqueous hydroxide. 

In addition to the already generalized couplings of aryl iodides, bromides, and chlorides, in 2003, the coupling of activated fluorides with boronic acids was reported (Table 2, entry The coupling with pseudohalogens has... 

The addition of the pseudohalogen iodine azide (prepared from iodine monochloride and sodium azide in acetonitrile) to methyl 5,6-dideoxy-2,3-di-0-p-tolylsulfonyl-a -L-arabtno-hex-5-enofuranoside has also been achieved a crystalline /3-iodo azide was isolated, in 69% yield, that was stable in the dark, but became colored on exposure to light.130 Brimacombe and coworkers133 have reported the addition of iodine azide to 5,6-dideoxy-l,2-0-isopropylidene-o -D-xy/o-hex-5-enofuranose X-ray crystallographic analysis established that the product is 6-azido-5,6-dideoxy-5-iodo-l,2-0-isopropylidene-/3-L-idofuranose. 

A similar situation is found in 6-azido-5,6-dideoxy-5-iodo-1,2-0-isopropylidene-/3-L-idofuranose, prepared by the action of iodine azide (IN3 a pseudohalogen) on 5,6-dideoxy-l,2-0-isopropylidene-a-D-xylo-hex-5-enofuranose.53 The addition of iodine azide to the... 

There are three important routes to the formation of the mercury-transition metal bond (a) displacement of halogen or pseudohalogen from mercury(II) salts with carbonyl metallate anions (b) reaction of a halo-phenylmercury compound with a transition metal hydride and (c) oxidative addition of a mercury halide to neutral zero valent metals.1 We report here the syntheses of three compounds containing three-centre, two-electron, mercury-ruthenium bonds utilizing trinuclear cluster anions and mercury(II) halides.2-4... 

A number of different polar and nonpolar covalent bonds are capable of undergoing the oxidative addition to M( ). The widely known substrates are C—X (X = halogen and pseudohalogen). Most frequently observed is the oxidative addition of organic halides of sp2 carbons, and the rate of addition decreases in the order C—I > C—Br >> C—Cl >>> C—F. Alkenyl halides, aryl halides, pseudohalides, acyl halides and sulfonyl halides undergo oxidative addition (eq. 2.1). 

The use of the pseudohalogen nitryl iodide, prepared in situ from iodine and silver nitrite, has been found to add to an alkene in what is strictly an anti-Markownikov fashion. The explanation for this lies in that nitryl iodide adds in a radical manner, initially forming the more stable secondary radical after addition of NO2.115 Treatment of 3-0-acetyl-5,6-dideoxy-1,2-0-isopropylidene-a-D-xy/o-hex-5-enofuranose with nitryl iodide was found to afford an unstable adduct, with the nitro group appended to C-6, and iodine attached to the more substituted C-5.116-118 Similarly, treatment of benzyl 2-0-benzyl-3,4-dideoxy-a-D-g/ycero-pent-3-enopyranoside (70, Scheme 19) with nitryl iodide afforded the unstable adduct 71, which, upon exposure to mild base (NaHC03), afforded the eliminated product, namely benzyl 2-0-benzyl-3,4-dideoxy-4-nitro-a-D-g(ycew-pent-3-enopyranoside (72). The eliminated product was then readily converted into benzyl 2-0-benzyl-3,4-dideoxy-(3-L-r/ireo-pentopyranoside (73) by reduction with sodium borohydride. Addition of deuteride using NaBD4 led to axial deuteration atC-3. 

The use of iodine-containing pseudohalogens has been demonstrated to cause a variety of side reactions. Treatment of methyl 5-0-benzoyl-2,3-dideoxy-3-D-g/ycero-pent-2-enofuranoside (83, Scheme 22) with nitryl iodide afforded none of the desired addition product, but gave a quantitative yield of furfuryl benzoate (86). The same result was obtained by treating 83 with iodine nitrate, or with iodine alone.125 The rationale for this undesired result lies in the ability of iodine to act as a Lewis acid, polarizing the glycosidic bond, generating an oxacarbenium cation, which then decomposes to the stable aromatic 86. 

Addition of Pseudohalogens to Unsaturated Carbohydrates. Part III. Synthesis of 3-Deoxy-3-C-nitromethyl-D-allose, a Branched-chain Nitro Sugar, W. A. Szarek, J. S. Jewell, I. Szczerek, and J. K. N. Jones, Can.]. Chem., 47 (1969) 4473-4476. 

Addition of pseudohalogens, such as BrNs and INS, to unsaturated compounds has been shown to occur either by a free radical (via N3) or by an electrophilic (via X+) stepwise mechanism, depending on the reaction conditions (Hassner and Boerwinkle, 1969). Electrophilic addition of BrNs to l-phenylpropyneisnon-regiospecifio (Hassner, 1909) and both products 50 and 51 are formed. The addition of IN3 is instead... 

The relatively high electron affinity of Au (EA = 2.3 eV) suggests that Au could behave as a pseudohalogen in forming negatively charged ions. In addition, Au (electronic coirfiguration [Xe] 4f " 5d 6s ) is isoelectronic with Hg . A few alkali metal amides M+Au are known (M = Na, K,... 

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