Carbon monoxide extrusion

Of mechanistic interest in this context is the independent generation of di-ir-methane diradicals of 3-oxa-di-TT-methane systems which do not give the rearrangement, in order to probe whether such diradicals at least in principle are prone to give di-ir-methane products. For this purpose, the cyclopropyldicarbinyl diradical in equation (25) was generated via photochemical carbon monoxide extrusion. Indeed, the expected oxa-di-ir-methane product 2,5-dimethyl-4,5-epoxy-2-hexene was formed, as well as other products. 

Flash-vacuum pyrolysis of l,l,4,5,6,7,8-heptafluoro-l,2-dihydrocyclobuta[a]naphthalen-2-one (550 C) resulted in carbon monoxide extrusion and concomitant formation of the correspond-... 

Beside carbon monoxide extrusion acyl radicals formed in a a-cleavage reaction can stabilize by subsequent hydrogen migration. Thus the a-trimethylsilylmethyl substituted cyclopentanone used by L. F. Tietze gives in a clean photochemical reaction the corresponding aldehyde with a vinylsilane moiety in its side chain. 

Thiirane 1,1-dioxides extrude sulfur dioxide readily (70S393) at temperatures usually in the range 50-100 °C, although some, such as c/s-2,3-diphenylthiirane 1,1-dioxide or 2-p-nitrophenylthiirane 1,1-dioxide, lose sulfur dioxide at room temperature. The extrusion is usually stereospeciflc (Scheme 10) and a concerted, non-linear chelotropic expulsion of sulfur dioxide or a singlet diradical mechanism in which loss of sulfur dioxide occurs faster than bond rotation may be involved. The latter mechanism is likely for episulfones with substituents which can stabilize the intermediate diradical. The Ramberg-Backlund reaction (B-77MI50600) in which a-halosulfones are converted to alkenes in the presence of base, involves formation of an episulfone from which sulfur dioxide is removed either thermally or by base (Scheme 11). A similar conversion of a,a -dihalosulfones to alkenes is effected by triphenylphosphine. Thermolysis of a-thiolactone (5) results in loss of carbon monoxide rather than sulfur (Scheme 12). 

Some insertion reactions, particularly those of carbon monoxide, are reversible, but many are not. Reactions have also been reported which result in extrusion of Y from M—Y—X, even though the reverse of this process [Eq. (1)] is not known to occur. Elimination of Nj from arylazo... 

This chapter is concerned initially with kinetic results and mechanistic interpretations of the CO insertion (Section III) and extrusion (Section IV) reactions. A discussion of the stereochemical data follows (Section V), and a comprehensive survey of these reactions by the triads (Section VI) rounds out the review. Carbon monoxide insertion reactions were discussed in 1967 by Basolo and Pearson (21). Since then they have been mentioned in several reviews (49, 118, 203, inter alios) but have not been treated comprehensively. 

Dehmlow49) found that the photochemical extrusion of carbon monoxide from the cyclobutene dione system is possible as exemplified by the conversion of diethyl squarate (43) to diethoxy cyclopropenone (44) ... 

Dimethylallene reacted with tetraphenylcyclopentadienone to produce methy-lenecyclohexadiene derivative 180 [146]. The cycloaddition occurred at the more substituted double bond of the allene, which was followed by extrusion of carbon monoxide from the intermediate 179. 

A rather novel application of the Diels-Alder reaction is the synthesis of dendrimers. Mullen and coworkers116 made cyclopentadienone 161 react with SA AA -tetraethynylbi-phenyl 162. This afforded, after extrusion of carbon monoxide, a first generation dendrimer 163 containing 22 phenyl rings (equation 45). Cyclopentadienone 161 reacted only as a diene, since the bulky triisopropyl groups prevented the ethynyl functions from reacting. 

Cobalt, as its CpCo(CO)2 complex, has proven to be especially suited to catalyze [2 + 2 + 2] cycloadditions of two alkyne units with an alkyne or alkene. These cobalt-mediated [2 + 2 + 2] cycloaddition reactions have been studied in great detail by Vollhardt337. The generally accepted mechanism for these cobalt mediated cycloadditions, and similar transition metal mediated cycloadditions in general, has been depicted in equation 166. Consecutive co-ordination of two triple bonds to CpCo(CO)2 with concomitant extrusion of two molecules of carbon monoxide leads to intermediates 578 and 579 via monoalkyne complex 577. These react with another multiple bond to form intermediate 580. The conversion of 578 to 580 is said to be kinetically favored over that of 579 to 580. Because intermediates like 580 have never been isolated, it is still unclear whether the next step is a Diels-Alder reaction to form the final product or an insertion to form 581. The exact circumstances might determine which pathway is followed. 

Extrusion of carbon monoxide from the [44-2]7t cycloadducts of 2//-azirines and cyclo-pentadienones (Scheme 29) constitutes another useful synthesis of 3//-azepines. Careful experimentation reveals that loss of CO from the encfo-adduct is concerted with the disrotatory cleavage of the C—N bond, and that no azanorcaradiene intermediate is formed... 

Photochemically induced extrusions of carbon monoxide generate 1,2-dithietanes in equilibrium with their valence bond tautomers, dithiones (Scheme 19) (74JA3502). 

We shall find that this reaction is again a rather special anomaly, needing special treatment, but there are straightforward 6-electron cheletropic reactions, such as the irreversible extrusion of nitrogen from the diazene 2.176, and the easy loss of carbon monoxide from norbornadienone 2.177. 

Tetraene 165, with the dienes separated by two two-atom linkages, undergoes photocycloaddition to give the strained 166 (Sch. 37) [112]. Double extrusion of carbon monoxide from 167 yields tetraene 168 with the dienes separated by two three-carbon chains. This tetraene yields pentacyclic 169 in 50% overall yield [113]. 

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