Silyl diazomethanes

Elimination of trimethylchlorosilane and nitrogen occurs when the (phos-phino)(silyl)diazomethane la is reacted with para-toluenesulfinyl chloride at low temperature. The formation of the four-membered heterocycle 92, obtained in 87% yield, can be rationalized by a multiple-step mechanism involving the formation of the (phosphino)(sulfinyl)carbene 2v. The insertion of the (phosphoryl)(sulfenyl)carbene 91, resulting from a 1,3-oxygen shift from sulfur to phosphorus in 2v, into a carbon-hydrogen bond of a diisopropylamino group readily accounts for the formation of 92.84... 

Summary Trimethyl- and triisopropyl-silyl diazomethane derivatives have been used for the synthesis of new types of diazo derivatives including those featuring a heavier main-group element or a transition metal directly bound to the diazo-carbon. They are also precursors to a variety of stable nitrilimines and carbodiimides, and stable pseudo-diazoalkenes and carbenes. (Phosphino)(silyl)carbenes have been used in the synthesis of new types of heterocycle including some stable four-7c-electron four-membered derivatives. 

It is clear from the known diazoalkane reactivity pattern [14] that only derivatives R R C=N2 can be employed that do not react with phosphines (cf. Section 3.2.10.5). Transformations can be observed for the easy-to-handle diazoacetates and diazomalonates as well as for a number of other compounds, e. g., trimethyl-silyl diazomethane. Aryldiazoalkanes, however, form phosphazenes that do not release the alkylidene group. Another problem can arise from the (catalytic) formation of ketazines - again, unreactive byproducts. 

Phenyl(trimethylsilyl)carbene can be generated by gas-phase pyrolysis of phenyl(trimethyl-silyl)diazomethane (1) at 500 °C (see Houben-Weyl Vol. El9b, p 1427). An attempt to trap this carbene with 2,3-dimethylbuta-l,3-diene furnished cyclopropane 3 only in trace amounts besides products 2, 4, and 5. Cyclopropane 3 can be prepared independently and in better yield by photolyzing the diazo compound in the presence of the butadiene. Thermally induced ring expansion of 3 provides cyclopentene 4, a fact that explains the low yield found under pyrolysis conditions. 

The mixture becomes yellow which is the color of trimethyl silyl-diazomethane. 

The continuing development of solid-phase synthesis and combinatorial chemistry has led to solid-phase oxazole syntheses with a minimum of purification. Iso and co-workers generated ot-(trimethylsilyl)diazoketones on a Wang resin and employed rhodium-catalyzed diazo transfer methodology to prepare oxazoles (Scheme 1.47). Reaction of the resin-bound benzoyl chloride 169 with (trimethyl-silyl)diazomethane gave the corresponding a-(trimethylsilyl)diazoketone 170 in excellent yield. Treatment of 170 with an aryl nitrile in the presence of catalytic Rh2(OAc)4 then furnished a resin-bound 2,5-diaryl-4-(trimethylsilyl)oxazole 171. 

The rippertene diterpenes are of current interest due to the condensed tetracyclic 16-carbon atom core and the presence of several quaternary carbons. The following synthesis starts with isopulegol and passes through a silylated diazomethane-induced regioselective ring expansion (Scheme 50) [87]. 

Triisopropylsilyl)diazomethane. Silylation of diazome thane with TIPS triflate and diisopropylethylamine in ether at —20 °C to 25 °C gives a 45% yield of (triisopropylsilyl)diazome-thane (eq 8). This silylated diazomethane is used to prepare stable silyl-substituted nitrilimines. ... 

This is followed by hydrolysi.s of the ester moieties with potassium carbonate and reesterification of the carboxy moiety with diazomethane to produce intermediate 65. The solitary free alcoholic hydroxyl at C-9 is oxidized with Collins reagent and the silyl ether groups are removed with acetic acid to give enprostil (63) [15]. 

Reaction of lithiated silyl- and diaminophosphino-diazomethanes (30, R = Me3Si, (R 2N)2P) with triphosphenium salt, [((Me2N)3P)2P]+BPh4 to give the respectively substituted [l,2,4]diazaphospholes has also been described to take place via the corresponding phosphaalkynes. Triphosphino substituted [l,2,4]diazaphosphole has been obtained by thermolysis of the phosphino-phosphiranyl-diazomethane via the... 

The many derivatizing reagents commercially available include methanolic HC1 and diazomethane for methylation, and iV,(9-bis(trimethylsilyl)trifluoroacetamide (BSTFA), with or without 1% trimethylchlorosilane (TMCS), for silylation. Using BSTFA, hydroxyl moieties also can be silylated, giving the corresponding trimethylsilyl ethers. 

Although methylation of 2(l//)-pyrazinones with diazomethane gives a mixture of O- and N-methylated pyrazines as the fixed tautomers (Equation 20) <1993JOC7542>, the trimethylsilylation leads to the exclusive formation of 0-silyl compounds, which are effectively converted to bromopyrazines 42 (Scheme 33) <1999JHC783>. In the same... 

Ketenes rarely produce [3+ 2]-cycloaddition products with diazo compounds. The reaction possibilities are complex, and nitrogen-free products are often obtained (5). Formation of a cyclopropanone represents one possibihty. Along these lines, the synthesis of (Z)-2,3-bis(trialkylsilyl)cyclopropanones and (Z)-2-trialkylsilyl-3-(triethylgermyl)cyclopropanones from diazo(trialkylsilyl)methanes and appropriate silyl- or germylketenes has been reported (256,257). It was found that subsequent reaction of the cyclopropanone with the diazoalkane was not a problem, in contrast to the reaction of diazomethane with the same ketenes. The high cycloaddition reactivity of diazomethylenephosphoranes also extends to heterocumulenes. The compound R2P(C1)=C=N2 (R = N(/-Pr)2) reacts with CS2, PhNCO and PhNCS to give the corresponding 1,2,3-triazole derivative (60). 

Using diazomethane as the limiting reagent, silyl- and germyl-substituted ketenes5-7 in certain cases gave cyclopropanones which were isolated as stable compounds.5,6 Transformations of trimethylsilylketene and triethylgermylkelene to the 2- and 3-substituted cyclobutanones was accomplished in 90 and 82% yield, respectively. Mild reaction conditions (— 78 °C) in diethyl ether solutions were employed. 

In situ ring enlargement of intermediate cyclopropanones to silyl- and germyl-substituted cyclobutanones was achieved by treatment of silyl- and germyl-substituted ketenes 12 with an excess of diazomethane.129,130... 

Gas chromatographic separation has not gained wide acceptance in spite of being quite sensitive and specific. This mode of separation is complicated by the need for derivatization of sulfonamide residues before gas chromatographic analysis. These drugs are subjected to derivatization via methylation with diazomethane (223, 224, 253, 254, 271), or double derivatization via methylation followed either by silylation with Ai-methyl-Ai-trimethylsilytrifluoroacetamide (261) or by acylation with A-methyl-bis(trifluoroacetamide) (256). This derivatization step is required not only to form the volatile derivatives of the sulfonamides but also to improve their chromatographic properties (thermal stability and decreased polarity). 

Diazocarbonyl compounds can also be prepared by C-acylation of diazoalkanes with polystyrene-bound acyl halides (Entry 6, Table 10.19). As an alternative to diazomethane, the more stable a-(trimethylsilyl)diazomethane may be used, which is sufficiently nucleophilic to react with acyl halides. On heating, the resulting a-(trimethyl-silyl)diazo ketones undergo Wolff rearrangement to yield ketenes, and have also been used as starting materials for the preparation of oxazoles [368]. 

---