Hypervalent iodine, with alkenes

Under certain conditions, amides can add directly to alkenes to form N-alkylated amides. 3-Pentenamide was cyclized to 5-methyl-2-pyrrolidinone by treatment with trifluorosulfonic acid. Acylbydrazine derivatives also cyclized in the presence of hypervalent iodine reagents to give lactams. When a carbamate was treated with Bu3SnH, and AIBN, addition to an alkene led to a bicyclic lactam. 

Treatment of aryl-substituted alkenes with hypervalent iodine compounds can lead to the formation of phenyliodinated intermediates, which can be stabilized by the aryl substituent via the formation of phenonium ions. Subsequent nucleophilic attack might then lead to rearranged products. This behavior can be nicely seen by comparing the unsaturated carboxylic acids 78 in their reaction with (diacetoxyiodo)benzene 3. The substrate 78a without the phenyl substituent is cyclized to the phenyliodinated intermediate 79, which is then attacked by the acetate under the formation of lactone 81 [142]. Substrate 78b is, however, then stabilized by the formation of an intermediate phenonium ion 80 and attack by the acetate is accompanied by a 1,2-phenyl migration and 82 is generated, Scheme 35 [143]. 

Dinitro-6-phenyliodonium phenolate (146) is a stable iodonium zwitterion484. It reacts under photolytic conditions with various alkenes, alkynes and aromatic compounds to afford 2,3-dihydrobenzo[ ]furans, benzo[6]furans and 6-aryl-2,4-dinitrophenols. The mechanism involves hypervalent iodine compounds (iodinanes, 147) and is illustrated for the reaction with an aromatic compound (equation 127). Compounds 148 are the major products when ArH = PhH, PhOCH3 or 1,4-dimethoxybenzene. With furan and thiophene, 149 is the principal product. The reaction does not proceed with chlorobenzene and nitrobenzene. 

Wc-Ditosylates are formed from alkenes on reaction with the hypervalent iodine reagent 50. Enantioselectivity is moderate. 

Reactions of alkenes with hypervalent iodine compounds lead mostly to vicinally functionalised alkanes. This is the case with PhI(OAc)2, PhIO, PhI(OH)OTs, PhI(OTf)0(TfO)IPh and other related reagents.230,231,233,239-247 poj. example, treatment of alkenes with PhI(OH)OTs, (HTIB), affords vie bis(tosyloxy)alkanes with a syn stereospecificity.239,241 n generally admitted that this reaction proceeds by the electrophilic attack of the hypervalent iodine species on the ethylenic double bond to afford a carbonium ion intermediate (140). This intermediate undergoes two consecutive Sn2 substitution reactions to eventually give the final products. (Scheme 5.17)... 

Cross-couplings. The Stille coupling of organostannanes with hypervalent iodine compounds has a broad scope. Diaryl and dialkenyl tellurides are also active toward alkenes if the catalytic system contains AgOAc. ... 

The structure and reactivity of several specific classes of hypervalent iodine compounds have been investigated theoretically. Varvoglis, Tsipis and coauthors have studied the geometry and electronic stmcture of some hypervalent iodine compounds PhIX2 by means of extended Hlickel and CNDO/2 quantum chemical approaches [200], The bonding was analyzed in terms of both the model of delocalized MOs on the basis of interactions between fragment MOs derived from EHMO-SCCC calculations and that of localized MOs derived by the CNDO/2 method. The ability of these compounds to afford c -addition products with alkenes via a synchronous molecular addition mechanism was found to be theoretically feasible [200]. 

Dichloroiodo)benzene can be convenientiy generated in situ from other hypervalent iodine reagents and used for subsequent chlorination of organic substrates. In a specific example, an efficient chlorination of p-keto esters, 1,3-diketones and alkenes has been performed using iodosylbenzene with concentrated HCl, selectively giving a-chloro-p-keto esters, 2-chloro-l,3-diketones and 1,2-dichloroalkanes, respectively [63]. A stereoselective anti-addition was observed in the chlorination of indene under these conditions. 

If the oxidation is performed in the presence of an external dienophile, the respective products of [4+2] cycloaddition are formed [351-356]. Typical examples are illustrated by a one-pot synthesis of several silyl bicyclic alkenes 283 by intermolecular Diels-Alder reactions of 4-trimethylsilyl substituted masked o-benzoquinones 282 generated by oxidation of the corresponding 2-methoxyphenols 281 [351] and by the hypervalent iodine-mediated oxidative dearomatization/Diels-Alder cascade reaction of phenols 284 with allyl alcohol affording polycyclic acetals 285 (Scheme 3.118) [352]. This hypervalent iodine-promoted tandem phenolic oxidation/Diels-Alder reaction has been utilized in the stereoselective synthesis of the bacchopetiolone carbocyclic core [353]. 

C-H borylation is a widely used methodology for the synthesis of organoboronates [63-65]. Most of the applications have been presented for the synthesis of aryl-boronates. However, functionalization of alkenes has also attracted much interest [66, 67]. In most applications, iridium catalysis was used. However, in case of alkenes, borohydride forms as a side product of the C-H borylation, which undergoes hydroboration with alkenes. This side reaction can be avoided using palladium catalysis under oxidative conditions. In a practically useful implementation of this reaction, pincer-complex catalysis (Ig) was appHed (Figure 4.17) [51]. The reaction can be carried out under mild reaction conditions at room temperature using the neat aUcene 34 as solvent. In this reaction, hypervalent iodine 36, the TFA analog of 29, was employed. In the absence of 36, borylation reaction did not occur. 

Isoxazoles display a range of biological activities, such as anti-inflammatory, antimicrobial, anticancer, and antinociceptive, that justify a constant effort in the development of new synthetic strategies. New syntheses of isoxazoles 1 and isQxazolines 2 via 1,3-dipolar cycloaddition (1,3-DC) of alkynes and alkenes with nitrile oxides were described (130L4010). The 1,3-dipoles were generated by oxidation of aldoximes catalyzed with hypervalent iodine species formed in situ from catalytic iodoarene and oxone as a terminal oxidant, in the presence of hexafluoroisopropanol (HFIP) in aqueous methanol solution. 

Zhdankin and coauthors [92] showed that nitrile oxides 119 can be generated by hypervalent iodine-catalyzed oxidation of aldoximes 118 using oxone as a terminal oxidant (Scheme 29). These in situ generated nitrile oxides 119 reacted with several alkenes and alkynes to afford the corresponding isoxazolines 121 and isoxazoles 120 in moderate to good yields. 

To date, this chemistry remains rather unexplored with respect to the development of related transition metal catalyses [43]. Still, difunctimialization of alkenes with hypervalent iodine reagents has been explored extensively over the past few decades [44], and there are important recent contributions that indicate that hypervalent iodines can indeed serve as suitable chiral reagents or catalysts for enantio-selective oxidation of alkenes [43-46]. 

Addition of two nitrogen moieties to an alkene was initially reported within the historic diazidonation reaction. In 1986, Moriarty reported such a diazidonation using PhIO as the terminal oxidant in combination with NaNa and in AcOH as solvent, which allowed for facile diazidonation of several alkenes [58]. Unfoitu-nately, functional group tolerance was a major problem and, as the consequence of the underlying radical mechanism for the double bond oxidation, the corresponding diazide products were obtained as diastereomeric mixtures. More defined conditions to generate the hypervalent iodine(III) compound PhI(N3)2 were used by Magnus, which provided an advanced diazidonation protocol [59-62]. 

Alkene substrates on oxidation with hypervalent iodine reagents allow various transformations depending on their structure and on the reaction conditions. Some of these reactions using chiral hypervalent iodine reagent are reported to be stereoselective. As described earlier, the Wirth group developed new chiral... 

Zhdankin et al. reported the iodine(III) catalyzed oxidative cycloaddition of aldoximes 60 with alkenes and alkynes to prepare isoxazoles and isoxazolines. The active hypervalent iodine(III) species was generated in situ by the oxidation of catalytic 3,5-dimethyliodobenzene using Oxone as an inexpensive and environmentally safe terminal oxidant in aqueous 1,1,1,3,3,3-hexafluoroisopropanol (HFIP). This activated iodine(III) promoted the oxidation of the corresponding aldoximes efficiently affording nitrile oxides 61, which upon cycloaddition reaction with various alk5mes 62 and alkenes 64 resulted in isoxazoles 63 and isoxazolines 65, respectively in moderate-to-excellent yields (up to 92%). In this oxidative conversion, HFIP is believed to increase the electrophilicity of I(III) reagent (Scheme 11) [27]. 

A. Yoshimura, K.R. Middleton, A.D. Todora, B.J. Kastem, S.R. Koski, A.V. Maskaev, V.V. Zhdankin, Hypervalent iodine catalyzed generation of nitrile oxides from oximes and their cycloaddition with alkenes or alk)mes, Org. Lett. 15 (2013) 4010-4013. 

An oxidative rearrangement may take place when alkenes and ketones are treated with some oxidants, such as thallium(III)" and hypervalent iodine(III). When applied to cyclic alkenes and ketones, ring contraction may be observed, as discussed in the following paragraphs for selected examples mainly regarding the total synthesis of biologically active compounds. 

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