Butadiene monoxide, 3 + 2-cycloaddition

Dinitrogen-fused heterocycles have been formed in high yield by thermal 3-1-2-cycloadditions of two types of azomethine imines with allenoates. Rhodium-catalysed formal 3 -l- 2-cycloadditions of racemic butadiene monoxide with imines in the presence of a chiral sulfur-alkene hybrid ligand have furnished spirooxindole oxazolidines and 1,3-oxazolidines stereoselectively. ° Formation of 1,2-disubstimted benzimidazoles on reaction of o-phenylenediamine with aldehydes is promoted by fluorous alcohols that enable initial bisimine formation through electrophilic activation of the aldehyde. 

When (67) was treated with a wide variety of cycloaddition reagents under various conditions, it behaved as a diene or a dienophile but not as a 1,3-dipole. As a dienophile it reacted with 2,3-dimethyl-1,3-butadiene to give (70) and with cyclopentadiene to give an analogous product. As a diene it reacted with [2.2.1] bicycloheptene to give (72), presummably via (71), by loss of carbon monoxide and hydrogen. No products were isolated when (67) was treated with maleic anhydride, dimethyl acetylene-dicarboxylate, diphenylacetylene, dimethyl fumarate, carbon disulfide, isobutyl vinyl ether, cyclohexene, and cyclopentene. 

An interesting example of photochemically-mediated [4+2] cycloaddition was found for 115 (Sch. 26), which does not undergo cycloaddition with butadiene 3 thermally. Irradiation is believed to transiently expel carbon monoxide, leading to co-ordination of butadiene to the iron (116). The diene is then delivered intramolecularly, to form 117 [80]. 

Extrusion (or elimination) of sulfur from thiiranes and thiirenes is a facile process. Virtually all thiiranes and thiirenes, as well as their V-oxides and V,V-dioxides, undergo thermal extrusion of the sulfur moiety with increasing facility according to the trend S << SO < S02. Sulfur monoxide produced in this way can be utilized in cycloaddition processes, for example, from 2 in refluxing toluene with 2,3-dimethyl-l,3-butadiene in a chelotropic addition <1997JOC8366>. 

The synthesis and chemistry of thiirane-1-oxides (episulfoxides) was reviewed in 1997 by Abu-Yousef and Harpp <1997SR1>. One of the many interesting processes discussed there is the thermolysis of thiirane-l-oxide 122, at temperatures exceeding 100 °C, to generate sulfur monoxide. The latter is very reactive and can be trapped by cycloaddition to 1,3-dienes such as 2,3-dimethyl-l,3-butadiene 123 (Scheme 21). 

C5Me5)Ru(/ -butadiene)Cl reacts with butadiene in the presence of tri-fluoromethanesulfonic acid silver salt, and carbon monoxide reacts to afford 1,5-cyclooctadiene of [4 + 4]cycloaddition product as shown in eq. (16.26) [74]. If the... 

The further reaction patterns of 1,4-dicopper-l,3-butadienes 54 were expanded by investigation of the annulation of 54 with carbon monoxide. This reaction led to cycloaddition reaction and afforded expected cyclopentadienones 20 as well as the... 

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