Heterocumulene preparation

Molina P, Alajarin M, Vidal A (1989) ortho-Pyrrolylphenyl heterocumulenes preparation and cyclization to fused pyrroles. Tetrahedron Lett 30(21) 2847-2850. doi 10.1016/S0040-4039 (00)99141-X... 

A (pentamethylcyclopentadienyl)iridium chelating guanidinate complex has been conveniently prepared by treatment of [Cp IrCl2]2 with N,N, N"-th-p-tolylguanidine and base in THF at room temperature followed by recrystallization of the green product from toluene and pentane (Scheme 154). Insertion reactions of the product with heterocumulenes (diaryl carbodiimides, aryl isocyanates) have been investigated. It was found that the complex serves as highly active catalyst for the metathesis of diaryl carbodiimides with each other and for the more difficult metathesis of diaryl carbodiimides with aryl isocyanates (cf. Section V.C). ... 

Brus and co-workers produced nanoparticles of CdSe from the pyrolysis of the single-molecular cadmium selenate precursor [Cd(SePh)2].392 The similar metal(benzylthiolate) compounds [M(SCH2C6i Is)2] (M = Zn, Cd) were also used in the solid-state preparation of ZnS and CdS particles and produced mixtures of the hexagonal and cubic phases of the crystallites, with sizes of 5nm, on thermolysis between 200 °C and 400 °C under nitrogen.393 The bis(trialkylsilyl)chalco-genides [(Me3SiE)2Cd] (E = S, Se), prepared by heterocumulene metathesis as in Equation (11), were used to produce nanoparticles. If the reactions are carried out in TOPO, TOPO-passivated CdE nanoparticles can be obtained although there was little control over particle size 394... 

A full account of the preparation and 1,3-dipolar cycloaddition reactions of this class of meso-ionic heterocycle (105) has now been published. Using olefinic dipolarophiles or heterocumulenes, a number... 

Many of the compounds of this type have been prepared by interaction of cumulene ylides witli heterocumulenes and these are covered in a review by Bestmann <77AG(E)349>. The oxetane system 5 results from reaction of Ph3P=C=C=S with aryl isocyanates, ArNCO <77AG(E)349>. An unusual approach to an oxetane ylide is the reaction of DMAD with CO2 and two equivalents of methyl phosphite which gives 6 <81CC607>. 

Iminophosphoranes have also proved to be key intermediates because they react with carbonyl compounds, isocyanates, isothiocyanates, acid chlorides, carbon dioxide, and carbon disulfide to give a wide range of imines and heterocumulenes, which are intermediates to pteridines. The preparation of iminophosphoranes has been investigated... 

The highly reactive 2-azadiene with an allene and heterocumulene structure 126, prepared by gas-phase thermolysis of propargyl thiocyanate, has been found by the Banert group to be an efficient precursor for thiazole derivatives by nucleophilic-induced heteroannulation through carbon and... 

Isocyanates and isothiocyanates are highly reactive heterocumulenes, and are usually only prepared on solid phase as intermediates for the synthesis of ureas, carbamates, thioureas, etc., using methods similar to those used in solution (Table 14.2). 

In the case of amine nucleophiles, the products from the reaction with co-ordinated cyanates are carbamates or ureas (Fig. 4-34), and this provides a particularly convenient method for the preparation of carbamate complexes. An example of this behaviour is seen in the reaction of 3,5-dimethylpyrazole with cyanate in the presence of copper(n) salts (Fig. 4-35). Similar reactions are observed with co-ordinated thiocyanates and other heterocumulene s. 

The [2+2] cycloaddition of the Si=Si double bond of disilenes across a hetero double bond belongs to the most typical reactions for the preparation of disiletanes. Reaction of the supersilyl stabilized disilene 90 with PhHC=0 and Ph2C=S gave oxa- and thiadisiletanes 91 and 92, respectively (Scheme 15). The use of heterocumulenes 0=C=0 and 0=C=S in a similar cycloaddition reaction yielded oxa- and thiadisiletanes 44 and 31. The isolated disiletanes are colorless and oxygen, water, and thermostable compounds <2002CEJ2730>. 

Preparation of Heterocumulenes from Carbonic Acid (Derivatives)... 

The oxidation of fV-carbamoylimidazolidine-2-thiones (281) has been used to prepare 2,3,5,6-tetrahydroimidazo[l,2-cf][l,2,4]thiadiazol-3-ones (282) which undergo cycloaddition reactions with heterocumulenes to give a variety of heteropentalenes (81T2485). 

Dihydro- 1,3-oxazines (398) are cyclic intermediates in the synthesis of a-amino-y-oxo acid esters by reaction of acyliminoacetates with enamines derived from six-membered ketones240. Sulfur-containing heterocycloadducts 399 and 400 have been prepared by [4 + 2] cycloaddition of enamines to heterocumulenes like thioacyl isocyanates and acyl isothiocyanates241. 

Zirconaaziridines react with unsaturated C-C bonds such as (1) olefins and acetylenes [20], and with unsaturated C-X bonds such as (2) aldehydes and imines [20], (3) heterocumulenes [21,43,49],and (4) carbonates [21,22,43,50] (Scheme 5). The products generated upon workup are a-functionalized amines. Asymmetric transformations can be carried out when a chiral zirconaaziridine or inserting reagent is used optically active allylic amines and amino acid esters have been prepared, and the details of these transformations will be discussed. 

A variety of synthetic methods for preparing selenocarbonyl compounds have been developed, and recent reviews disclosed details of each compound in Scheme 1 [2b, 6, 8c, 9,11]. Accordingly, the synthetic methods are classified based on the reaction patterns rather than the types of compounds in this review. In particular, attention has been paid to the step of the formation of the carbon-selenium bond. The selenium atom has generally been introduced electrophilically or nucleophilically to the organic molecules. Additionally, heterocumulenes involving selenium atoms have been used as a starting material. 

A tandem aza-Wittig/heterocumulene-mediated annulation route was developed for the efficient production of 6,7,8,9-tetrahydro-benzothieno[2,3-r/]-l,2,4-triazolo[l,5-a]pyrimidin-10(3F/)-ones <05S1601>, and an amine oxide rearrangement was key to the regioselective preparation of pyrrolo[2,3-J]pyrimidines <0581164>. Hexahydro-2-phenacylidene-pyrimidines gave -lactam fused 8-aroyl-2,3,4,5-tetrahydro-7-hydroxy-6//-pyrrolo[l,2-a]py-rimidine-6-ones when treated with (COCl), in the presence of NaH <05IJH87>, and methyl... 

Amidostannanes containing the groups Sn-NC(=0)R or Sn-NS(0)2R are easier to prepare and to handle than are the aminostannanes. The acidity of the proton on nitrogen in the parent amide is now sufficient for reaction to occur with organotin hydroxides, oxides, and alkoxides (and aminotin compounds), and, once formed, the amidostannanes are less sensitive to moisture. A variety of amidostannanes is also available from the addition of Sn-0 and Sn-N bonded compounds to nitrogen heterocumulenes. 

Other zwitterionic 18-electron d°-anionic metallocene complexes 26-29 with one Zr-heteroelement cr-bond can be prepared following the same strategy. This implies the treatment of 16a with an equimolecular amount of heterocumulenes (C02, CS2, Cy-N=C=N-Cy, R-N=C=S, R-N=C=0) (Scheme 7) [29]. It is also reasonable to propose here that the formation of all these new systems is due first to a nucleophilic attack of the free phosphine of 16a at the electrophilic center of the organic substrate. In the second step, cyclization reaction on the coordi-natively unsaturated metal center occurs to form the stable pentavalent anionic zirconocene products. With isocyanates and isothiocyanates, the anionic charge... 

Other heterocycles prepared using iminophosphoranes include novel py-rimidinone and quinazoline derivatives, obtained from in situ aza-Wittig reactions of N aryl-iV-(triphenylphosphoranylidene)carboxidamides (114) and ketenes, and pyridothienopyridazines and pyrimidothienopyridazines, accessed from aza-Wittig/electrocyclic-ring closure reactions between phos-phoranes (115) and (116) and heterocumulenes. ... 

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