Allene derivatives cascade reactions

An interesting annelation reaction of allene-derived 13-dipoles with 3-(IV-aryliminomethyl)chromones 38 affords, in fair yields, after [4 +3] cycloaddition and a subsequent cascade of rearrangements, derivatives of the novel iV-aryl-2,3-dihydro-4-ethoxycarbonylchromano[2,3-h]azepin-6-one system 39 (for example, R = Me, R1 = Cl) (Scheme 9). In the initial cycloaddition, the substituted chromone acts as an azadiene moiety <00OL2023>... 

Grigg and Xu have developed a variety of so-called queuing cascades involving allenes. The intra-intermolecular carbopalladation sequence of the <9-iodo-A-methyl-A -(methylallyl)aniline 142 and 1,1-dimethylallene 143 with subsequent / -dehydropalladation leads to the 1,3-dienyl-substituted indole derivative 144, which is immediately trapped by an added dienophile (e.g., A-methylmaleimide) in a Diels-Alder reaction to yield 145 (Scheme 37)7 ... 

A one-pot sequential and cascade sequence involving the formation of allylic azides, from aryl/heteroaryl/vinyl halides, allene and sodium azide, by palladium catalyzed anion capture, and cyclization-anion capture, followed by 1,3-dipolar cycloaddition provided a variety of 1,2,3-triazoles in good yields <01T7729>. Reaction of a,P-acetylenic aldehydes 107 with sodium azide in dimethylsulfoxide followed by hydrolysis afforded 5-substituted-4-carbaldehyde-1,2,3-triazole derivatives 108 <01TL9117>. 

Palladium-catalyzed cyclization of allenes bearing a nucleophilic functionality has also been used widely for the construction of various types of heterocycles, and several cascade sequences were developed based on this cyclization reaction. Ergot alkaloids have been reported to exhibit broad biological activity, and several synthetic derivatives, such as pergolide and bromocriptine, were also used as antiprolactin and... 

Benzannulated enyne-allenes with heteroatomic substitution in the allene branch are precursors of the indeno-fused heteroatomic systems that are suitable for use in pharmacological applications. Introducing a heteratomic substituent in the allene branch of the enyne-allenes promotes a cascade of reactions that lead to derivatives such as 1 OH-indeno [1,2-g] quinoline, 9H-fluorene[2,3- ] furan, 9H-fluorene[2, 3-b]thiophene, 5H- and 6H-indeno[2,l-/]indolizine [278]. An example of this strategy is the synthesis of indeno-fused derivatives of quino-lizinium salts 3.558 (Scheme 3.41) [278]. 

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