Iodination result

Dioxopiperazines are amongst the most ubiquitous of natural products (75FOR(32)57) and they are formally derived by the cyclodimerization of a-amino acids (69CCC4000) or their esters. A number of methods are available for their oxidation to the corresponding pyrazines. Treatment of 2,5-dioxopiperazines with triethyl- or trimethyl-oxonium fluorobor-ate followed by oxidation with DDQ, chloranil or iodine results in pyrazine formation, usually in high yields (Scheme 63) (72JCS(P1)2494). 

The first representatives of this group of compounds, 1,5-benzotelluroazepinones 57, have been prepared in 17% yield by the reaction between 2-iodopropyolanilides and NaHTe (98H631). The reaction proceeds, most probably, as nucleophilic substitution of the iodine, resulting in telluroles 58 and the subsequent nucleophilic addition of a hydrotelluride group to the triple bond. An alternative mechanism involving initial addition of NaTeH to the triple bond followed by the nucleophilic substitution of the iodine atom was mled out because the anilides PhNHCOC=CR do not react with NaTeH under the conditions at which the heterocycles 57 were obtained. Neither of the adducts PhNHCOCH=C(R)TeH or [PhNHCOCH=C(R)Te]2 was isolated. 

Treatment of alkenyldialkylboranes with iodine results in the formation of the Z-alkene with migration of one boron substituent.26... 

Synthesis of the dihydrothiophene derivatives was described by Flynn et al. [70] (depicted in Scheme 23) and involved the conversion of 3-butynol 92 to benzyl 3-butynal sulfide 93. Sonogashira coupling of the sulfide 93 with acetic acid 5-iodo-2-methoxyphenyl ester 94, produced the intermediate 95. Treatment of compound 95 with iodine resulted in a rapid and... 

In the brine electrolysis system, silica is also contained in raw salt. Silica will precipitate on to membranes in the presence of calcium, strontium, aluminium and iodine resulting in the loss of current efficiency [8-10]. Silica can also be removed in a column filled with ion-exchange resin containing zirconium hydroxide, just like the iodide ion. 

The condnctivity measnrements indicate that when di-iodine is added to a solution of BZIM (5) (D=S), initially both the nentral (I) and the ionic (Ila) compounds are formed as it is shown in Scheme 13.3A. Fnrther addition of di-iodine results to the ionic complex (Ila). In the case of NMBZT (Scheme 13.3B) a cocrystallization of both the spoke and iodoninm complexes takes place prodncing only the iodonium complex, in excess of I. ... 

The Ag2 S ISE has Nemstian response dE/d log a( = 0.0296 V in the sulphide concentration range 10" to 10" M and silver ions from 10 to 10 M if the solutions are prepared from pure salts, as a further concentration decrease is prevented by adsorption on the glass (see p. 76 and [87, 163]). After prolonged use, the limit of the Nemstian behaviour shifts to about 10" m [130] as a result of formation of mixed potentials on accumulation of metallic silver in the membrane surface. An analogous deterioration in the membrane function in the presence of iodine results from surface oxidation [23]. Cyanide interferes only at large concentrations the equilibrium constant of the reaction... 

A deficiency of iodine results iu insufficient synthesis of thyroxine and a low plasma level, so that secretion of TSH is increased in an attempt to stimulate synthesis but this results in enlargement of the thyroid gland (goitre). Iodine deficiency in pregnancy impairs brain development in the foetus, causing mental retardation (known as cretinism). Indeed iodine deficiency is one of the major public health issues worldwide an estimated 200 million people are affected. 

Intramolecular addition of hydroxylamines and hydroxamic acids to the non-activated double bonds is possible through oxidative cyclization. Reaction of O-Acyl fi,y-unsaturated hydroxamates (e.g. 56, equation 38) with bromine provides 3,4-substituted iV-hydroxy -lactams such as 57 with high diastereoselectivity. Analogous reaction of O-benzyl hydroxylamine 58 (equation 39) with iodine results in five-membered cyclization with 2 1 ratio of diastereomers. ... 

Oxidation with iodine resulted in an octamethylferricinium-based anion-exchanger that was successfully used to separate oligonucleotides (dJu-dTis). 

Construction of LB films having lateral d.c. conductivities is a burgeoning activity. Results of published work are summarized in Table 9 [726-772]. The first formation of a conducting LB film was reported by French workers in 1985 [726]. Non-conducting LB films were formed from N-docosylpyridinium TCNQ. Subsequent exposure to iodine vapor resulted, however, in the lateral conductivities in the order of 0.1 S cm-1 [726]. The initially formed LB film was shown to consist of (TCNQ. )2 dimers whose molecular planes were almost parallel to the substrate. Iodination resulted in the development of a brown-purple color, the partial oxidization erf the radical anions to TCNQ° and, most importantly, a dramatic rearrangement of the LB film. In iodine-doped films, the TCNQ molecules have been shown to assume a position almost perpendicular to the substrate [721, 773],... 

This system (see Fig. 17) is unique in many aspects of the structure and dynamics and has historic roots for nearly 50 years since the seminal works by Hildebrand and Mulliken. Mixing of benzene and iodine results in a new color, a new absorption spectrum, and a new theory. 

Irradiation of 2-acetyl-l-benzylidine-l,2,3,4-tetrahydroisoquino-line (353 R = H) in methanol in the presence of iodine results in the formation in good yield of 8-methylprotoberberinium iodide (354 R = H)384 and not of the dehydroaporphane system which might be expected by analogy with oxidative cyclization of cis-stilbene... 

Several reactions of carbonyl compounds that have one or more a hydrogens proceed through the enol form. Reaction of ketones with chlorine, bromine, and iodine result in substitution of halogen for a hydrogen rates are typically first-order in ketone and independent of halogen concentration and even of which halogen is used. Racemization of ketones with asymmetric centers adjacent to the... 

The treatment of terminal and internal alkynes with 1-tosyloxybenziodoxolone (11) in the presence of molecular iodine results in trans iodo-oxytosylation of the C,C-triple bond, and in the case of unsymmetrical alkynes, leads to Markovnikov adducts (Scheme 18) [46]. Co-iodinations of alkynes with the... 

Tnmsannular cyclization of lactams.2 Photolysis of the 8-membered lactam 1 in cyclohexane containing C6H5IO and iodine results in the gem-diiodide 2 (m. p. 111°, 40%). But the same reaction with 9- or 10-membered lactams results in cyclization to oxoindolizidines or l-azabicyclo[5.3.0]decanones, respectively, in high... 

The use of GSR has been reported to effect deoxygenation of an a-hydroxy ketone.188 Treatment of methyl2,6-di-0-pivaloyl-a-D-ribo-hexopyranosid-3-ulose (147, Scheme 39) with triphenylphosphine, imidazole, and iodine, resulted in deoxygenation to afford methyl 4-deoxy-2,6-di-0-pivaloyl-a-D- ryf/i/w-hexopyranosid-3-ulose (148). Presumably the reaction proceeds via initial formation of the iodo compound, followed by loss of iodine through the enol form, a precedent for which has been reported.189... 

Reaction of a stable carbene with iodine results in compound 46, which can be considered an isolated transition state which models the nucleophilic attack of the carbene on the iodine molecule (Scheme 25).55 The iodine-iodine bond js significantly lengthened and the carbon iodine bond distance of 2.104(3) A is slightly elongated when compared to that of iodoarenes. The authors report that protic solvents promote ionic dissociation to the 2-iodoimidazolium ion which is isoelectronic with the tellerium adduct 44. 

An alternative method for the formation of acyl hypoiodites, developed by Barton, involves the treatment of the acid with r-butyl hypoiodite. Subsequent white light photolysis in benzene at room temperature gave good yields of it ides from primary, secondary and tertiary acids (equation 21). The method was not applicable in the presence of alcohols. A more recent technique involving hypervalent iodine is due to Suarez primary, secondary or tertiary aliphatic acids are heated to reflux in tetrachloromediane with iodosylbenzene diacetate and iodine resulting in good yields of iodides. The method is mild and, with obvious exceptions such as unprotected alcohols, is tolerant of many functional groups, as illustrated in equation (22). ... 

Treatment of the initial stannanc with potassium fluoride/iodine results in the stcreospecific preparation of the diiodidc 18. ... 

The iodolactonization of a n, .vyn-3,5-dimethyl-l,6-heptadiene-4-carboxylic acid (9) under kinetic conditions in dichloromethane, saturated aqueous sodium hydrogen carbonate and iodine results in excellent alkene and facial selectivity. In fact, of the four possible isomeric iodolac-tones only three are isolated in a 96.5 3.1 0.4 ratio, i.c., there is >99 1 group selectivity and 97 3 distereofacial selectivity, as determined by capillary GLC and 300 MHz H-NMR analysis37. 

Suli ur can be replaced by selenium use of chlorine or iodine results in lower yields. R. H. Cragg and A. F. Weston, Tetrahedron Letters, 655 (1973). 

We have requested Union Carbide Corp. (Tuxedo Park, New York) to supply us with Na I at a concentration of <400 mCi/ml in dilute NaOH. Since this request for Na I at a lower concentration, we have not noted any difficulties with 36 lots of radioiodine. The Na I in dilute NaOH gives reliable iodination results for as long as 2 months when stored just as received from the supplier, at room temperature. 

---