Triphenylphosphine-Iodine

Wipf and Miller have reported side-chain oxidation of 3-hydroxy amides with the Dess-Martin periodinane, followed by immediate cyclodehydration with triphenylphosphine-iodine, which provides a versatile extension of the Robinson-Gabriel method to substituted oxazoles. Application of this method was used to prepare the oxazole fragment 10 in 55% overall yield from 3-hydroxy amide 8. 

Halogenation of 106 with triphenylphosphine, iodine, and imidazole provided the iodo derivative 109. On treatment with lithium aluminum hydride, 109 was converted into two endocyclic alkenes, 110 and di-O-isopro-pylidenecyclohexanetetrol, in the ratio of 2 1. Oxidation of 110 with dimethyl sulfoxide - oxalyl chloride afforded the enone 111.1,4-Addition of ethyl 2-lithio-l,3-dithiane-2-carboxylate provided compound 112. Reduction of 112 with lithium aluminum hydride, and shortening of the side-chain, gave compound 113, which was converted into 114 by deprotection. ... 

Davies et al. describe the preparation of both oxazole- and thiazole-containing derivatives of combretastatin. By formation of the ketoamide intermediate 60, in a 54% yield (Scheme 14), both classes of compounds may be obtained by altering the last step of the reaction [58]. To produce the oxazole 61 a cyclo-dehydration reaction was performed using triphenylphosphine-iodine-triethylamine, and the thiazole compound 62 was formed by thiona-tion using Lawesson s reagent, with an excellent yield (94%). 

Several methods are available to access glycosyl iodides (Scheme 2.50). Anomeric hemiacetals bearing diverse protecting groups (Bn, Bz, Ac, N3, CMe2) upon treatment with a polymer-bound triphenylphosphine-iodine complex and imidazole can be converted into a-glycosyl iodides [179]. The precipitated by-products,... 

Another general route to 5,10-dihydro[l,2,4]triazolo[5,l-b]quinazolines via the electrocyclization of an azino carbodiimide intermediate has been described (94S1057). The key iminophosphorane, a benzophenone-1-[(triphenylphosphoranylidene)amino]ethylidenehydrazone, was easily prepared in a Kirsanov-variant first applied by Bayless and Zimmer (68TL3811). It consists of the reaction of triphenylphosphine/iodine/trieth-ylamine with benzophenone 1-aminoethylidenehydrazone (94SI057). 

ALKYL IODIDES Iodine monochloride. Triphenylphosphine-Iodine. Tung-sten(VI) chloride-Tctramethyltin. 

A modification of GSR has been reported by Classon and co-workers.190 The idea remains the same create a covalently bound phosphorus cation and displace with a nucleophile—in this case, a halogen. Both bromine and iodine have been used.190 Three different systems were evaluated (1) chlorodiphenylphophine, iodine-bromine, and imidazole (2) p-(dimethylamino)phenyldiphenylphosphine, iodine-bromine, and imidazole or (3) polymer-bound triphenylphosphine, iodine-bromine, and imidazole. The last two were found to be very similar to just triphenylphosphine itself, and displayed reactivity inferior to the first system. The polymer-bound reagent does allow for easier removal of triphenylphosphine oxide produced in the course of the reaction. As with the original procedure, and consistent with a Sn2 mechanism, inversion of configuration occurred. Again, as with the original method vicinal diols were readily converted into alkenes.191 This... 

Coupling of 15 with D-threonine methyl ester in the presence of PyBroP and DMAP gives the dipeptide 73. The oxazole 74 is formed after Dess-Martin oxidation and cyclodehydration with triphenylphosphine/iodine. After formation of the methylamide function, an iterative sequence of deprotection with TBAF and coupling with 15 leads to the dipeptide 75, then to the tripeptide 76 and finally to the tetrapeptide 77. The coupling reagent is PyBroP in each case. The overall yield (74 —> 77) is 21 %. After cata-... 

The authors also reported chemical shift assignments for one additional compound [92]. Refluxing the t-butyl substituted precursor of 66 in CH2CI2 with triphenylphosphine, iodine, and triethylamine led to the formation of the substituted p-carboline, 68... 

The desulfurization of imidoylthioureas can also be conducted with triphenylphosphine, iodine and triethylamine. The same reagents are used in the desulfurization of 5-imino-... 

Deoxygenation of sulfoxides and azoxyarenes. This combination is superior to triphenylphosphine-iodine for deoxygenation of sulfoxides to sulfides (70-95% yield) and of azoxy benzenes to azobenzenes ( 90% yield, two examples). The reaction can be promoted by addition of sodium iodide. One advantage is that the by-product, HMPT, is soluble in water and easily removed. 

ROH— RI The combination of triphenylphosphine and 2,4,5-tri-iodoimidazole in toluene at elevated temperature (120°) effects replacement of primary and secondary hydroxyl groups of carbohydrates by iodine with inversion of configuration. The reaction is heterogeneous and the carbohydrate need not be soluble in toluene. Triphenylphosphine, iodine, and imidazole can also be used, but the yields are generally lower. 

Nucleophilic Attack at Halogen. This field of activity continues to be dominated by applications of well-known phosphine-positive halogen combinations. Alcohols can be oxidised to the related aldehydes and ketones under mild conditions by the DMSO-Ph3PX2 system, which provides an alternative to the Swern oxidation." The triphenylphosphine-iodine system has been... 

Conversion to the corresponding iodide 124 was accomplished using a one step procedure involving the addition of 123 to a stirred solution of triphenylphosphine, iodine and imidazole in THF/MeCN. The stage was set for intramolecular alkylation a single product 125 formed immediately (70%) when iodide 124 was added to LDA at -78 °C. Unfortunately, deprotonation and cyclization occurred from Ca rather than Cb. Similar results were obtained independent of the counterion (e.g., NaHMDS,... 

Although most phosphorus chlorides and bromides are commercially available, it is sometimes necessary to prepare fresh reagents. In the case of phosphorus iodides, the reagents have poor shelf-lives (they are unstable and decompose under mild conditions) and are commonly prepared in situ, or immediately prior to use by reaction of red phosphorus with iodine. Phosphorus bromides can also be prepared this way. Reaction of 1,2,3-propanetriol with red phosphorus and bromine, for example, gave l,3-dibromo-2-propanol. 3 iodides are similarly prepared from red phosphorus and iodine, as in the conversion of cetyl alcohol (155) to cetyl iodide (156) in 85% yield. Using P and I2 is a common method for the conversion of aliphatic alcohols to aliphatic iodides. Another popular method is illustrated by treatment of 157 with triphenylphosphine, iodine, and imidazole,. In this case, taken from Hiemstra s synthesis of roseophilin, 67 the primary alcohol unit was converted to iodide 158 in 96% yield. 

The key to this approach was the formation of the oxazole ring in the presence of the thiazoline rings. Cyclization of 1298 with Burgess reagent" gave the expected intermediate oxazoline (not shown), but this could not be oxidized to 1299 using Ni02, NBS/benzoyl peroxide, or CuBr/tert-butyl perbenzoate. Thionyl chloride, phosphorus oxychloride, titanium tetrachloride, or triphenylphosphine/iodine did not effect cyclodehydration of the p-ketoamide produced from the Dess-Martin periodinane oxidation. 

The conversion of alcohols to iodides with inversion using triphenylphosphine-iodine-imidazole, or triphenylphosphine-2,4,5-tri-iodoimidazole, (4,157) has now been described in detail. The purity and yield of tertiary iodides (or bromides) prepared from the alcohols and aqueous HI (or HBr) at 0 can be improved by addition of lithium or calcium halides it is believed the metal salts retard competing hydrolysis of the tertiary halides. Secondary alkyl bromides have been prepared from the alcohols with retention of configuration via the inverted selenides (Scheme 35). Two other new reagents for the... 

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