Iodinolysis

Tab. 2-1 Hydroalumination-iodinolysis ofl-decene with BUS3AI in the presence of late transition metal compexes ...

The adducts derived from catechol borane are hydrolyzed by water to vinylboronic acids. These materials are useful intermediates for the preparation of terminal vinyl iodides. Since the hydroboration is a syn addition and the iodinolysis occurs with retention of the alkene geometry, the iodides have the -configuration.214... 

The coupled fragments were then converted to a vinyl iodide. The key steps were a Z-selective Lindlar reduction and iodinolysis of the vinyl silane, which was done using NIS in acetonitrile (sequence F-l to F-ll). 

Until recently, the structures of the five-membered zirconacycles had been proposed on the basis of NMR data and identification of the final organic compounds, especially the products of deuterolysis, iodinolysis, and carbonylation. Determination of their structures by X-ray analysis proved to be more difficult than that of three-membered zirconacycles, largely because attempts to obtain their stable 18-electron derivatives led to ring-contraction to give three-membered zirconacycles, as in the last example in Scheme 1.56. This difficulty was overcome by the use of bulky Cp derivatives that permitted the formation of stable, crystalline, 16-electron, five-membered zirconacycles such as 5 [198] and (tBujQHj Z Ch (6) [199] (Scheme 1.59). 

Conversion of silylenynes 102 [6] into the corresponding SnMe3 derivatives 103, followed by a Zr-promoted bicyclization, leads to the gem-stanniozirconocene derivatives 104. Car-bonylation gives 105, and subsequent iodinolysis of 105 gives 106 in good yield (Scheme 7.30). The formation of 106 proceeds with >98% stereoselectivity, thus allowing the synthesis of carbacyclin 107 [170,171]. 

The method enables conversion of substituted alkynes to (fc)-2-methyl-1 -alkenylalumi-num species, and, by subsequent iodinolysis, to the corresponding iodoalkenes with retention of the double-bond configuration. Depending on the substitution pattern of the starting alkyne, many useful products emerge from this reaction, which themselves can serve as building blocks for transition metal-mediated or -catalyzed coupling reactions [59—62]. 

Like chlorinolysis, the brominolysis and iodinolysis of diorganyl ditellurides offer a facile route to tellurium tribromides and triiodides. ... 

GLC analysis of a small aliquot after iodinolysis with Iodine... 

SCHEME 69. Pd-catalyzed dialkylation of 1-sila-l-zircona-l-alkenes via iodinolysis and its application to the synthesis of discodermolide183... 

By contrast, for iodide 18 having the triple bond activated by a phenyl group, conversion to the cyclic organozinc species 25 occurred effectively and the latter could be efficiently functionalized, provided that traces of moisture were excluded by pre-treatment of zinc powder with Mel. The substituted benzylidene cyclopentanes 26 and 27 were respectively obtained after iodinolysis and palladium-catalyzed cross-coupling reaction with benzoyl chloride (equation 10). However, it could not be assessed whether the formation of organozinc 25 was attributable to an anionic or a radical cyclization pathway (or both) as, had iodide 26 been produced by a radical iodine atom-transfer, it would have been converted to 25 by reaction with metallic zinc due to the presence of the activating phenyl group21. 

Similarly, if 5-iodo-l-pentyne (66) was converted to the alkynylethylzinc reagent 67, the subsequent Zr-promoted ethylzincation afforded the gem-diorganozinc 68 which was stable in dichloromethane. Replacement of the latter by a more basic solvent such as THF triggered a a-type cyclization process leading to the cyclopentenylzinc 69, as demonstrated by the formation of 70 after iodinolysis (equation 27)45. 

Internal alkynes were also viable substrates as illustrated by the ethylzincation of 5-decyne which led to the tetrasubstituted alkenyl iodide 71 after iodinolysis, as a single geometric isomer (syn addition) (equation 28)1 4. 

Zirconocene diiodide can promote the addition of diallylzinc to a,/1-disubstituted unactivated alkynes. Thus, in the case of 5-decyne, a 94/6 mixture of the two isomeric alkenyl iodides (derived respectively from syn and anti additions to the triple bond) was obtained after iodinolysis (equation 74)108. However, the stereoselectivity was lower for 2-butyne (80/20) and the case of unsymmetrical alkynes was not mentioned. 

A Pd-catalyzed type I zinc-ene reaction was used to construct the spirobicyclic core of the sesquiterpenoid (—)-erythrodiene 164117,118. Thus, the allylic acetate 165 was treated with Et2Zn in the presence of a catalytic amount of Pd(OAc)2 and as the ligand to afford, after iodinolysis, the spirobicycle 166 with high diastereoselectivity (equation 82). 

Additionally, some Pd-catalyzed type II zinc-ene cyclizations have been described. When the allylic acetate 181 was treated with EtiZn in the presence of a catalytic amount of Pd(PPh3)4, its slow conversion to a cyclic organozinc species by a type zinc-ene reaction was observed and iodinolysis afforded the six-membered ring 182 in relatively low yield. The regioselectivity was noteworthy as C-C bond formation occurred at the most substituted terminus of the allylmetal. By contrast, the type II palladium-ene cyclization of the allylic acetate 181, in conjunction with a /1-elimination process, proceeded with opposite regioselectivity and led to the six-membered ring 183 (equation 88)114. 

When the dimetallic species 210 was first deuteriated with MeOD and then subjected to iodinolysis, a 60/40 mixture of the two diastereomeric a-deuteriated iodides 267a and 267b was obtained. Although the use of a first small electrophile such as a MeOD did not enable efficient differentiation of the two carbon-metal bonds, a reversal of diastereose-lectivity was observed when the a-deuteriated dimetallic species 268 was first protonated with MeOH and then reacted with iodine. This result points towards the configurational stability of the resulting monoorganozinc species generated after reaction with a first electrophile, presumably due to the coordination by fert-butyl ether moiety (equation 127)162. 

When the first electrophile was not a ketone or an aldehyde, as illustrated for the reaction of 276 with crotonyl chloride, the intermediate chelated alkenylmetal 278 could also be subjected to iodinolysis or palladium-catalyzed cross-coupling reactions with aryl and alkenyl iodides in the presence of a stoichiometric amount of CuBr as a promotor as well as a polar cosolvent such as IV, IV-di methyl acetamide (DMA) (equation 131)165 166. 

By contrast, when the first electrophile was an aldehyde as illustrated for the reaction of 276 with benzaldehyde, the resulting alkenylmetal presumably became part of a six-membered ring alkoxide 279 and hence so poorly reactive that it did not even react with iodine. However, treatment with Me3SiCl resulted in the silylation of the secondary zinc alkoxide and allowed iodinolysis to subsequently proceed, affording the (Z)-alkenyl iodide 280 (equation 132)165. Unfortunately, this protocol was not efficient for tertiary alkoxides generated by initial reaction of 276 with ketones. 

An extension of this strategy to the preparation of pyrrolidines has been reported199,200. The tertiary amine 390 could be metallated with f-BuLi in ether and, after transmetallation with ZnBr2, the zinc-ene-allene took place leading, after hydrolysis or iodinolysis, to the disubstituted pyrrolidines of type 391 as single diastereomers (equation 169). 

Bromoboration (Z)-/>2-dihalo-l -alkenes1 Reaction of a terminal alkyne (1 -octyne) with BBr3 in CH2C12 results in a p-bromoalkenylborane, which undergoes brominolysis or iodinolysis with retention to provide (Z)-l,2-dihalo-l-alkenes (equation I). 

Early studies by Keller11 showed that iodinolysis of alkylmercuric iodides by iodine in solvent dioxan was free-radical in nature in the presence of air or oxygen the kinetic form was second-order in iodine and zero-order in alkylmercuric iodide. Addition of iodide ion altered the kinetic form to first-order in alkylmercuric iodide and first-order in I3, that is second-order overall. Winstein and Traylor12 studied the iodinolysis of 4-camphylmercuric iodide (IV) by I2/I in... 

Values of K, the equilibrium constant for reaction (4), are given in Table 2 and it can be seen that in the solvents commonly used for kinetic studies, values of K are around 104-107 l.mole-1. Since kinetic studies are usually carried out with a large excess of iodide ion, such values of K result in almost complete conversion of iodine into I3 , and at any time during a kinetic run [I2] [I3 ]. Hence for reaction (3) the decrease in the concentration of organometallic substrate RMX , denoted by R, will equal the decrease in [I3 ], and the velocity, v, of the iodinolysis may thus be expressed as... 

---