Compounds containing Other Heteroatoms

The majority of the reports included in this section are concerned with the photoreactions of organosilicon compounds. In particular, the generation and reactions of silylenes (silanediyls) have been the subject of much interest. A variety of organosilylenes have 

2-cyclopropyl-2-phenylhexamethyl-trisilane. Silylene itself reacts rapidly with alkenes but is virtually unreactive towards alkanes.  

Di-t-butylsilylene (186), generated by photolysis of hexa-t-butylcyclotrisilane (187), adds readily to the nitrile group of 

A high yield of the expected silylene insertion product 

The practice of surrounding reactive double bonds with bulky substituents has made it possible to isolate disilenes as thermally stable, yellow or orange coloured, crystalline species. 

The generation and reactions of silylenes (silanediyls) have again attracted attention. The decay of dimesitylsilylene, 

The key to the synthesis of stable disilenes, which are readily obtained by dimerization of silylenes, is protection of the silicon-silicon double bond by substituents. 1,2-Di-(1-adamantyl)dimesityldisilene (198), a disilene which is resistant 

Photoreactions in which the silicon atom plays a less important role have also been reported. Type I cleavage with loss of carbon monoxide is observed on irradiation of benzyl dimethyl- 

Other reports of note in silicon-containing systems 

10-dicyanoanthracene-sensitised photoreaction of the polyalkanol (157), silicon-silicon cleavage occurs via a transient radical cation efficient intramolecular trapping by the hydroxyl affords the silyl ether (158) 

The photochemical breakdown of polysilanes is of current interest in view of the importance of these compounds as photoresists. Three pathways have been identified in the photodecomposition of permethyl oligosilanes, namely, silicon-silicon bond cleavage, chain abridgement by elimination of a silylene (a silanediyl), and chain scission with formation of a silylene. The persistent radicals observed on irradiation of poly(di-n-alkyl- 

Products derived from the two silenes (163) and (164), formed by competing 1,3-trimethylsilyl migrations, were obtained on irradiation of l-(3,4-dihydro-2H-6-pyranyl)-1-phenyltetramethyl-disilane (165)Separate studies have shown that silenes are intermediates in the photorearrangement of analogous benzenoid disilanes. 1,4-Bis(pentamethyldisilanyl)naphthalene (166), however, behaves in a different fashion, and in the absence of a trapping agent is converted on irradiation into the trisubstituted naphthalene (167) In the presence of methanol, the adduct (168) is also obtained the proposed pathway is outlined in Sotaeme 8. 

1- Dimesityl-2,2-diphenylsilene (169) can be prepared by irradiation of the novel air-stable disilathietane (170). In contrast, the disilanylbenzoquinones (171) undergo photochemically induced conversion into the silyl ethers (172) in alcohols and into the silicon heterocycles (173) in the presence of ketones, in both transformations via the unstable sila-m-quinones (174). o-Silaquinone methides are intermediates in the photoreactions of 

Photoreactions initiated by Norrish Type II pathways have been observed in cyclopropyl silyl ketones,and Type I cleavage is responsible for the conversion of the trimethylsilyl ketones (183) into the allylsilane carboxaldehydes (184)the latter transformation is facilitated by the presence of the silicon atom which stabilises a radical in the j8-position. 

Much of the interest in this section is again centred around the 

Photochemically induced cleavage of hexa-t-butylcyclo-trisilane (213) affords di-t-butylsilanediyl (214) and tetra-t- 

The generation and reactions of silenes have attracted attention. Photoisomerization of the mesitoylsilane (218) affords 

Photocycloaddition to silicon-containing alkenes occurs efficiently and is a valuable synthetic procedure. The photoaddition of 1,2-bis(trimethylsiloxy)cyclobutene to cyclohex-2-en-1-ones, for example, has been employed in the stereocontrolled synthesis 

Photoreactions have also been reported in organophosphor-us, organoselenium and organoboron compounds. Photochemically 

The photoinduced generation and reactions of dimethylsilylene, McjSi, continue to attract attention. The insertion of dimethylsilylene, prepared by irradiation of dodecamethylcyclohexasilane, into the oxygen-hydrogen bond of alcohols to yield alkoxydimethylsilanes has been used to probe the effect of solvent on dimethylsilylene react vity. Dimethylsilylene is more selective in diethyl ether or tetrahydrofuran than in hydrocarbon solvents and this has been attributed to the formation of complexes between dimethylsilylene and donor solvents. Kinetic studies of the insertion reactions of dimethylsilylene have been undertaken. Previous investigations have resulted in the isolation of dimethylsilylene in an argon matrix at 10 K. Further irradiation of dimethylsilylene (299) under the same conditions gave 2-silapropene (300), which in turn is converted into the dimer (301) at 50K.  

Methylphenylsilylene (302), generated photochemically from 2-phenylhepta-methyltrisilane (303), undergoes addition and insertion to 2,3-dimethylbutadiene to give the alkene (304) and the diene (305), respectively, whereas dimesityl- 

Fischer, and D. Skrodzki, Z. Anorg. Allg. Chem., 1980, 466, 29. 

Compounds containing C=Si bonds have again been prepared photochemi-cally. Species of this type have been proposed as intermediates (307) in the phototransformation of some di- and tri-substituted silacyclobutanes (308) in 

Irradiation of tris(trimethylsilyl)phenylsilane in the presence of hex-l-yne and other alkynes affords the corresponding silacyclopropenes. Those silacyclopropenes formed from monosubstituted acetylenes undergo further photoisomerization to disilanylacetylenes via a 1,2-hydrogen shift. Two competing pathways have been observed on irradiation of the disilabicyclo[2.2.2]octa-2,5-diene 

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REACTIONS OF ORGANOBROMINE COMPOUNDS CONTAINING OTHER HETEROATOMS... 

A,B-Diheteropentalenes have only limited solubility in water. The hydrogen donor properties of the NH site of pyrrole and the hydrogen acceptor property of the oxygen atom of the furan ring can increase the solubility of the compounds containing these heteroatoms relative to the systems with only sulfur or selenium atoms in their structure. Alkylation at the nitrogen of furo[3,2-6]pyrrole derivatives increases the solubility in ethanol and other organic solvents. 

Dimroth-type rearrangements are well documented in fused pyrimidines such as in [l,2,4]triazolo[4,3-a]pyrimidines and [l,2,4]triazolo[4,3-c]pyrimidines under acid or alkaline conditions. The same type of reaction will occur in pyrimidines fused to azoles containing other heteroatoms. Thus, the pyrimidines (695) undergo the Dimroth reaction under both acid and alkaline conditions to furnish the rearranged compounds (696) (74JOC3783). 

Some trinuclear clusters are also known among diorganotin carboxylates. These are summarized in Table 2.4.2. It can be seen that the carboxylic acids involved in the formation of these compounds are mono/dicarboxylic acids containing other heteroatoms (Table 2.4.2, entries 1-5, 8 and 9) or dicar-boxylic acids without other heteroatoms (Table 2.4.2, entries 6 and 7). Among the cyclic compounds. 

The ring systems described in the present chapter contain other heteroatoms, and the normal Hantzsch Widman rules are applied. Compounds (10) are therefore diazaphosphinines. The order of precedence in heteroatom numbering should be noted oxygen > sulfur > nitrogen > phosphorus. In this chapter we normally place the P atom at the bottom of the ring, but this is seldom position 1, when other heteroatoms are present. 

Monocyclic lactams containing other heteroatoms, such as compound 171, give chloroenals (Eq. 141). There are numerous examples of Vilsmeier reactions with lactams fused to benzene rings representative products are 172 and 173 (Eq. 142), 174 (Eq. 143), " 175 (Eq. 144),and 176 (Eq. 145). "... 

Boduszynski and co-workers [114] and Andersson and Sielex [115] have used GC-AED to examine the sulfur-containing molecules in petroleum and its heavier processed products. Both groups found a preponderance of thiophenic sulfur compounds in processed materials, in contrast to petroleum. The unprocessed petroleum had mercaptans, sulfides, thiophenes, as well as other species containing other heteroatoms in addition to the sulfur. These two studies also showed that this detector has the selectivity for sulfur that is attainable with the two older commonly used sulfur detectors, the flame photometric detector (EPD) and the chemiluminescent detectors. The first of these, however, suffers from a very non-linear response. This effect is very compound-class dependent. This is due to the fact that the light-emitting species that is detected is a two-sulfur atom one that results from recombination of the sulfur atoms in the combusted sample peak. The efficiency of combustion and the rate of recombination are both dependent on the... 

For which compounds containing a heteroatom (an atom other than carbon or hydrogen) does the molecular ion have an even-numbered mass For which does it have an odd-numbered mass ... 

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