Antimony ylides—

The ylides have been classified on the basis of the heteroalom covalently bonded to the carbanion. Accordingly, they can be differentiated into nitrogen ylide (Scheme 2), sulfur ylide Scheme 3, phosphorus ylide Scheme 4, arsenic ylide Scheme 5, antimony ylide (Scheme 6), bismuth ylide (Scheme 7) and thallium ylide (Scheme 8). 

It is obvious from the literature summarized in recent reviews (11, 26) that very little information is available on ylidic compounds of antimony. Moreover, the few compounds synthesized were all taken from the aryl series, whereas those of the alkyl series appear to be completely unknown. Even the aryl antimony ylides were of very limited thermal stability and could only be isolated in special cases (11). 

Noted added in proof More recent experiments have shown (59) that up to five tri-methylsilylmethyl groups can also be introduced at the antimony-V center, and, e.g., compounds of the type (CH8)nSb[CH2Si(CHj)j]s can be easily obtained. Among the decomposition products of pentakis-trimethylsilylmethyl-stiborane (n = 0) a high yield of tetramethylsilane has been detected. This observation suggests that an antimony ylide may be among the primary products of this decomposition, but such a species could not be isolated ... 

Copper-catalyzed thermal reaction of diazo-trifluoropyruvate 301 with aryl aldehydes in the presence of SbBu3 provides alkenes 302, which are transformed to racemic amino acids 304 (see Scheme 9.65) [96]. Antimony ylide 305 is proposed as an intermediate. 

Ylides from R N2. This reagent is more effective than bis(acetylacetonate)-copper(II) (5, 244) for generation of carbenes from diazo compounds.2 The decomposition proceeds at a lower temperature, even at room temperature. The mild conditions are particularly useful in the preparation of heat-sensitive ylides, such as those of antimony, bismuth, and tellurium. 

Carbon functional groups, attachment to polysilanes, 3, 585 Carbon-heteroatom bond formation via antimony(III) compounds, 9, 428 via antimony(V) compounds, 9, 432 via bismuth(III) compounds characteristics, 9, 440 with copper catalysts, 9, 442 non-catalyzed reactions, 9, 443 with bismuth(V) compounds, 9, 450 with bismuthonium salts, 9, 449 with bismuth ylides, 9, 450 Carbon-heteroatom ligands in tetraosmium clusters, 6, 967 in tetraruthenium clusters, 6, 960... 

When this method is applied to compounds of phosphorus and arsenic, the components undergo an entirely different reaction, and alkylidene trialkyl derivatives of these elements (ylides) are obtained 102, 104). Thus, instead of the introduction of an additional alkyl substituent at the central element, as observed with antimony, a deprotonation at one of the a-carbon atoms adjacent to phosphorus and arsenic occurs ... 

These derivatives have not only provided new synthetic pathways but have shown improved thermal stability (as in the case of arsenic ylides) and a modified pattern of chemical reactivity. The donor properties of ylides 55, 24), and most of their synthetic applications 103), have been covered in other reviews and articles 3, 26) and are not duplicated here. The general organometallic chemistry of arsenic, antimony, and bismuth is the subject of the invaluable monograph by Doak and Freedman 11). The broad scope of phosphorus ylide and pentaorganophosphorane chemistry was covered in the leading multivolume series on organophosphorus chemistry edited by Kosolapoff and Maier 3, 21). Finally, the recent... 

The difference between the ylides (39) and the tetraphenylcyclopentadienylide is that the former, but not the latter, have substituent groups, carbonyl or sulphonyl, which can interact intramolecularly with the antimony or arsenic atom. This interaction has been clearly shown by X-ray crystal structures ... 

These X-rays studies show that the interaction is greater in the case of antimony than in the case of arsenic. Despite the greater size of antimony than arsenic, the Sb — O distance is shorter than the As—O distance. In addition the Sb—C (ylidic) and As—C(ylidic) bond distances indicate that the Sb—C bond has more double-bond character than the As—C bond. In all cases these ylides take up Z,Z-conformations, both in solution (as observed by NMR spectra) and in the solid state, but in the solid state they are not symmetric, only one of the substituent groups being involved in the intramolecular interaction. This can be represented as in 40 and 41. In accord with such structures one of the bonds linking substituents to the ylidic carbon atom is shorter than the other. 

The oldest syntheses of chrysanthemates are those starting from 2,5-dimethyl-2,4-hexadiene (238). There have been more papers on the use of rhodium or antimony to catalyze the addition of diazoacetate and chiral copper complexes to create asymmetry during the addition (see Vol. 4, p. 482, Refs. 219-222). The problem with this route is to avoid the use of diazo compounds. An old synthesis of Corey and Jautelat used the ylide addition of a sulfurane to a suitable precursor (in this case a C3 unit was added to methyl 5-methyl-2,4-hexadienoate, 239), and a recent paper gives details about the addition of ethyl dimethylsulfuranylideneacetate to 2,5-dimethyl-4-hexen-3-one (240). This led exclusively to the tran -isomer 241, from which ethyl trans-chrysanthemate (185, R = Et) was made. Other ylide additions are mentioned below. 

A variety of ylides (e.g. 5) of arsenic, antimony and bismuth have been prepared under mild conditions via the reaction of diazo compounds with the appropriate three valent organometalloid. Schmidbaur s group continues to produce new ylide structures, for example (6).5 The lithiated aza-ylide (8) has been prepared directly from the parent... 

Arsenic, Antimony, and Bismuth.- (Diphenylarsino)methyl-lithium (203) has been prepared by either halogen-lithium or tin-lithium exchange from (204) or (205) respectively. Interestingly the reactivity of (203) depends on the method of preparation used, although the reasons for this are not known. A stereoselective synthesis of JE-a, -unsaturated aldehydes has been achieved by reacting aldehydes with the arsonium salt (206) in the presence of a weak base. The ylide derived from (206) shows a reasonable... 

Phosphorus compounds as well as other currently used flame retardants containing nitrogen, antimony, sulfur, etc., have two unpaired electrons capable of reacting with carbenes to give more or less stable ylides... 

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