Tungsten amides

Tungsten complexes, 3, 973-1015 alkoxy carbonyl reactions, 2, 355 alkyl alkoxy reactions, 2, 358 amides... 

Tungsten aryloxo complexes have been shown to catalyze the intramolecular metathesis reactions of di- and tri-substituted co-unsaturated glucose and glucosamine derivatives to yield bicyclic carbohydrate-based compounds containing 12- and 14-membered rings [108,214,215]. An example is shown in Eq. 37. The tolerance for amides and esters is noteworthy, as are the yields and the size of the rings that are formed. 

Although the structure of the complex arising from I52/CH2CI2 is not clear, this catalyst is excellent in terms of ease of preparation. The catalyst is very active for formation of cycloalkynes with ring sizes different from those of diynes (Table 6.5). In contrast to tungsten alkylidyne complex 150, catalyst 152/ CH2CI2 is sensitive toward an acidic proton such as amide proton and exhibited remarkable tolerance towards many polar functional groups (Table 6.5). 

The aminocarbonylation of alkynes has been less explored as compared to that of alkenyl and (hetero)aryl halides. Nevertheless, several noteworthy applications of this reaction have been reported, including the syntheses of 2-ynamides, chiral 2-carbamoyl-7r-allylic tungsten complexes, angular triquinanes, 2-(carbamoylmethylene)tetrahydrofurans, alle-nyl amides, and others. ... 

In NaxW03-yFy Doumerc (1978) observed a transition that has all the characteristics of an Anderson transition similar phenomena are observed in NaxTayW3 y03. The results are shown in Fig. 7.14. It is unlikely that this transition is generated by the overlap of two Hubbard bands with tails (Chapter 1, Section 4) this could only occur if it took place in an uncompensated alkali-metal impurity band, which seems inconsistent with the comparatively small electron mass. We think rather that in the tungsten (or tungsten-tantalum) 5d-band an Anderson transition caused by the random positions of Na (and F or Ta) atoms occurs. The apparent occurrence of amiD must, as explained elsewhere, indicate that a at the temperature of the experiments. Work below 100 K, to look for quantum interference effects, does not seem to have been carried out. 

A solution of amide (0.053 mmol) in a mixture of CH2C12 (1.5 ml) and cyclohexane (1.5 ml) containing iodosylbenzene (0.106 mmol) and iodine (0.064 mmol) was irradiated with a tungsten lamp for 80 min at room temperature. After the reaction, the mixture was poured into chloroform, and washed with aq. Na2S03 solution, and dried over Na2S04. After removal of the solvent, treatment of the residue by column chromatography (eluent hexane/ethyl acetate = 85/15) produces cyclized sugar in 75% yield [53]. 

The metathesis of symmetrical aliphatic carbodiimides is also catalyzed by tungsten imido complexes above 140 Other carbodiimide metathesis catalysts include Cr(ll)/Si02/ iminophosphoranes, imido circonocenes, guanidine supported titanium complexes and group 14 amide complexes. ... 

A,A-Disubstituted aminocarbenes can be prepared directly by reaction of chromium, tungsten, molybdenum pen-tacarbonyl, and iron tetracarbonyl dianions with tertiary amides in the presence of chlorotrimethylsilane (Scheme 5). 

Tungsten alkylidenes have also been shown to accomplish carbonyl alkylidenation. Aldehydes, ketones, esters and amides have been used as the carbonyl moiety. These reactions involve metallacycle intermediates and appear to parallel much of the metathesis chemistry (equation 32). 

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