Koser reagent

Cycttzation. The bridging of piperazine derivative at an a-position of a nitrogen atom to an indole nucleus requires dual activation of two types of C—H bonds. Achieving the transformation with PhI(OH)OTs [Koser reagent] in one step, albeit in low yields, is quite gratifying. ... 

Ring contraction. Illustrated by the transformation of l-aryl-l,2-dihydronaphtha-lenes to indanes the Koser reagent has the same ability as T1(N03)3 but of course its use avoids the issue of toxicity. 

Muniz and co-workers prepared a series of substituted indoles (e.g., 76) using a modified Koser reagent that was made from iodosobenzene and 2,4,5-tris-isopropylbenzene sulfonic acid (77, TIPBSA). The hypervalent iodine reagent was used either stoichiometrically or in catalytic amounts with mCPBA as the terminal oxidant. A variety of N-protecting groups were tolerated and substituents on the aryl ring of 75 include halogens, carbonyls (aldehydes, ketones, esters), alkynes, and nitriles (HAG(I)7349). 

Antonchick and colleagues made use of PIDA to craft a series of 1-arylcarbazoles (Scheme 7, equation 1) [17], and Muniz s team employed iodosobenzene and 2,4,5-tris-isopropybenzene sulfonic acid (TIPBSA) as a modified Koser reagent to synthesize indoles (equation 2) [18],... 

In contrast, Muniz reported an indole synthesis from 2-vinyl anilines 13, which relies on activation of the alkene moiety by the hypervalent iodine reagent [9]. The reaction employs a sterically congested Koser reagent generated in situ from iodosobenzene and the bulky sulfonic acid 15. The reaction provides synthetically unique access to 2,3-unsubstituted indoles 14 and can also be conducted under catalytic conditions. 

G. F. Koser, Encyclopedia of Reagents for Organic Synthesis, John Wiley and Sons, Inc., L. A. 

The best known member among the various classes of these iodanes is undoubtedly [hydroxy(tosyloxy)iodo]benzene (HTIB), sometimes called Koser s reagent. It is prepared readily from (diacetoxyiodo)benzene and p-toluenesul-fonic acid monohydrate in acetonitrile. The same method using p-nitroben-zenesulfonic acid or 10-camphorsulfonic acid leads to the corresponding sul-fonyloxy analogs [41,42]. Of special interest are some iodanes of this type coming from a chiral ether. Their preparation was effected by direct oxidation with sodium perborate and the isolated diacetoxy derivatives were separately treated with p-toluenesulfonic acid in acetonitrile (Scheme 8) [43]. 

Flavanones - Isoflavones. Although Koser s reagent (1) is known to effect a-tosyloxylation of ketones,1 the reaction with flavanones (2) results in an oxidative 1,2-aryl shift to provide isoflavones (3) in 74-80% yield.2 This conversion has been effected previously with thallium salts. 

A catalytic amount of acid is sufficient, on the other hand, for the halogenation of activated aromatics such as polyalkylbenzenes by all the three NXSs. NIS iodinates mesitylene in presence of the very mild acid hydroxy(tosyloxy)iodobenzene (Koser s reagent, HTIB)7 2. NBS performs much better in the presence of / -toluenesulfonic acid and NCS shows the highest yields when trifluoromethanesulfonic acid is used as catalyst743. This difference in reactivity leads to a novel method for preparation of a mixed halogenated mesitylene (equation 100). 

Hydroxy(tosyloxy)iodo]benzene, Koser s Reagent... 

Applications to the synthesis of heterocyclic compounds of hypervalent organoiodine reagents are covered by Gerald Koser (University of Akron, Ohio) who is well known for his own book in the field. The present review provides continuity with the earlier comprehensive treatment of the subject by Moriarty and Prakmash in Volume 69 of Advances in Heterocyclic Chemistry, which covered the field up through 1996. 

Sin arly the a-mesyloxy esters are available by reaction with Koser s reagent. " Neither of these studies addressed the question of stereoselectivity. 

Lodaya, J.S.. and Koser. G.E. Alkynyliodonium salts as alkynylating reagents. Direct conversion of alkynylphenyliodoniiun tosylates to dialkyl alkynylphosphonates with trialkyl phosphites, J. Org. Chem., 55. 1513. 1990. 

Koser, G. F., The Synthesis of Heterocyclic Compounds with Hypervalent Organoiodine Reagents, 86, 225. 

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