Thermolytic conditions

The preparation and investigation of the thietane oxide system (5a) is largely associated with stereochemical and conformational studies . The investigation of the thietane dioxides (5b) is substantially related to the chemistry of sulfenes , the [2 -I- 2] cycloaddition of which with enamines is probably the method of choice for the synthesis of 5b . The study of the thiete dioxide system (6) evolved, at least in part, from the recognition that the unstable thiete system 183 can be uniquely stabilized when the sulfur in the system is transformed into the corresponding sulfone , and that the thiete dioxide system is very useful in cycloadditions and thermolytic reactions. The main interest in the dithietane oxides and dioxides (7) appears to lie in the synthetic challenge associated with their preparation, as well as in their unique structural features and chemical behavior under thermolytic conditions . ... 

Pteridines have been prepared in good yields from 6-amino-5-nitrosouracils with Meldrum s acid in the presence of piperidine as catalyst under thermolytic conditions <06SC3085>. Novel 6-formylpterin derivatives have been synthesized and their neuroprotective effects studied <06OBC1811>. 

Treatment of 1-azirine (292) with catalytic quantities of dichlorobis(benzonitrile)pal-ladium(II) gave a quantitative yield of the indole (293) (77CC664). This transformation proceeds through the intermediacy of a 2 1 azirine-palladium chloride complex. Conversion of the 1-azirine ring to indoles under uncatalyzed thermolytic conditions provides a mechanistically interesting comparison with the Pd(II)-catalyzed conversions. The C—N bond cleavage in the latter is apparently accelerated as a result of the coordination of the azirine to palladium. 

Tetrachlorocyclopropene has been known for some time to be a reasonably reactive dienophile.4 Its thermal ring opening to perchlorovinyl carbene is in accord with the behavior of other cyclopropenes under thermolytic conditions,5 but the... 

Under thermolytic conditions the cycloheptatriene 481 and the silyl enol ether 482 were obtained in 46% and 24% yield, respectively, along with 29% of the unreacted starting compound, the acylpolysilane which is the precursor for the reactive silene (equation 160)". 

Reactions of more electrophilic SC12 with fluoroolefins under thermolytic conditions are not selective they always produce a mixture of sulfenyl and thiosulfenylchlorides, sulfides, and polysulfides, along with substantial amounts of products of alkane chlorination [135]. 

Cycloaddition under thermolytic conditions is another route to tricyclic /3-lactams. The 1,3-dipolar cycloaddition of oxazolidinone 98 with /V-phenylmaleimide to give 100 has been described (see Section 2.04.6.3). In a sealed tube at 100 °C the oxazolidinone 98 reacts with a cyclopentenone derivative to give the tricyclic isomers 378 and 379 in the yield ratio of 4 1 (Equation 52) <1999JHC1365>. 

Alkenyl as well as alkyl nitrenes can be produced both by thermolysis and photolysis. However, photolysis is preferred due to the more favorable reaction conditions such as low temperature and the ability to use of particular solvents, which avoid side reactions such as the polymerization observed under thermolytic conditions. However, in some cases, alkenyl nitrenes can only be generated by photolysis [14]. Photochemically generated alkenyl nitrenes normally react by intramolecular addition to the 7r-bond forming 2H-azirines at rather high yields (Sch. 3) [6d,15], in addition, the... 

Heteroaryl nitrenes can be produced by thermolysis and photolysis, however, the reaction pathways are fundamentally different [17]. Under thermolytic conditions, ring cleavage is obtained, however, photolytically... 

Rh(CO)4] with the neutral cluster Rh4(CO)i2 affords the trigonal-bipyra-midal anion [RhsCCO) ] under mild conditions 162). Similarly, the octahedral species [Fe6C(CO)i6] has been prepared by the condensation of [Fe(CO)4] with stoichiometric amounts of FefCOlj under thermolytic conditions, which are necessary for the generation of the carbide atom [Eq. (2)] 269). 

Scheme 25. Reactions of Os fCO), with C5H4RN (R = H, Me), PhCCH, and CH CHj under thermolytic conditions.

In solution, but not as a pure substance, 52 decomposes at room temperature additionally according to Thermolysis Pathway III into nitrogen and l,l-bis(trimethylsilyl)hydrazide, which, under thermolytic conditions. 

The analogous bismuth-selenium compounds, R2BiSeAr, disproportionate slowly at room temperature and afford preparatively useful yields under thermolytic conditions ... 

This reaction constitutes a method for the transformation of saturated cyclic or acyclic carbonyl compounds in three steps (silyl enol ether formation, halocarbene addition, rearrangement) to a,) -unsaturated carbonyl compounds with one-carbon ring enlargement or chain elongation, respectively. The rearrangement can be induced under acidic, basic, or thermolytic conditions, or with silver(I) salts. 

The chemistry of vinyloxiranes has been reviewed in the context of their rearrangements to dihydrofurans. The cases involving divinyloxiranes, commonly encountered in publications on the preparation of oxepins, have been summarized in a compilation(see also Section 2.4.5.). Butynyl-substituted oxiranes gave, under thermolytic conditions, a variety of tetrahydrofurans, as well as dihydrofurans. 

C, 15 min, 100% yield. A thermolysis in quinoline was found advantageous when acid-catalyzed cleavage resulted in partial debenzylation of a phenol. Thermolytic conditions also cleave the BOC group from amines. In the following case the furan was anticipated not to be stable to strong acid. "... 

This section describes the most commonly used methods used to cleave one or more bonds within the oxabicydic framework. Aspects of this subject have been surveyed in other reviews describing the synthetic utility of [4+2] and [4+3] cycloaddition reactions [1,25,119,122,123]. The retro-Diels-Alder reactions of oxabicyclo[2.2.1] compounds under thermolytic conditions resulting in the extrusion of furan, acetylene or other stable species will not be covered, but the interested reader is directed to a recent review on this topic [122],... 

Ring cleavage is known to occur under thermolytic conditions. Rearrangement of 2-substituted... 

NHC or by in situ deprotonation of IPr-HCl salt, SIAd, well as unsymmetrically substituted NHC. Very recently, Grubbs reported that various [(NHC)RuCl2(PCys)(CHPh)] could be obtained from the reaction of precursor (72) and 2-(pentafluorophenyl)imidazolidines, such as (20), under mild thermolytic conditions. Ru-indenylidene complexes (75)... 

The recent synthesis of a single-source molecular precursor containing aluminum with 0Si(0 Bu)3 and 02P(0 Bu)2 ligands provided an important step toward general use of molecular precursor routes to materials with more complicated stoichiometries. Indeed, it was shown that this new complex, [( Bu0)3Si0]2Al[p-02P(0 Bu)2]2Al(Me)0Si(0 Bu)3, was readily converted to homogeneous SiyAl/P/0 materials under mild thermolytic conditions via loss of isobutene, H2O, and CH4(Eq. 2) [58]. 

The relative ease of the cyclization step from A to C may also be linked to the nucleophilic or coordinative ability of the heteroatom bound to the metal. The reaction of 7 with diphenylacetylene (Ph2C2) leads to the seven-membered derivatives 68 and 69 after prior isolation of the monoinsertion product 24, treatment with a silver salt, followed by the usual thermolytic conditions. This is another rare example of an intramolecular formation of a C-S bond within the coordination sphere of a transition metal and a novel, albeit limited to one alkyne, route to the rare family of dibenzo[bd] thiepins. With the closely related 8, which differs from 7 only by the tertiary amine unit in the metallacyclic framework instead of a thioether function, a carbocyclic product 71 is obtained (see under carbocycle reactions, next section). The formation of the seven-membered S-heterocycles is attributed to the good coordinative ability of the thioether group in 7. The S-atom remains close to the vinylic carbon function before the cyclization. With the poorly coordinating, readily displaced amine function in 8, the N-atom is detached from the metal and ultimately affords a spirocyclic product (see Scheme 18). 

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