Alkyl intermolecular cycloaddition

Apart from alkyl acrylates, electron-deficient alkenes do not react with azine 6.136,137 Isolation of the zwitterionic intermediate (e.g.. 8) resulting from the first intermolecular cycloaddition allows a mixed crisscross addition, with the second cycloaddition performed between the dipole and various dipolarophiles.138-140... 

However, yields in the intermolecular cycloaddition reactions of vinylcarbene complexes, formed by intramolecular insertion of an alkynyl tethered metal carbene complex, are higher when molybdenum rather than chromium or tungsten carbene complexes are employed. Mild thermolysis (THF, 65 °C, 1 h) in the presence of ten equivalents of an electronically undemanding alkene directly leads to the 2-alkyl-2-(2-methoxycyclopentenyl)cyclopropanes 31. ... 

A number of scenarios, albeit multistep, are conceivable for the transposition of the (3-hydroxy ketone functionality present in lactam 61 to the isomeric version in lactam 60. Lactam 61 could be constructed by an aldol ring closure of 62, which in turn could be fashioned by another aldol-type cyclization within aldehyde 63. Finally, a Diels-Alder cycloaddition of silyloxydiene 65 with the 2-amidoacrolein 64 was expected to furnish 63. It should be noted that this intermolecular cycloaddition was expected to install not only the central 1 -alkyl-1 -aminocyclohexane substructure of FR901483 but also the electrophilic and nucleophilic components, appropriately tuned, for the pending sequential aldol cyclizations. 

In 2004, Jiang and Li reported an efficient intermolecular cycloaddition reaction of diazocarbonyl compounds with alkynes catalyzed by InCls in water, which delivered a range of pyrazole derivatives (Scheme 16.10) [15], This reaction was proposed to proceed by a domino 1,3-dipolar cycloaddition-hydrogen (alkyl or aryl, refer to the... 

Fused aromatic compounds such as polyacenes have attracted much attention as organic conductive materials. However, established methods are very limited. Lack of general and convenient synthetic methods for fused aromatic compounds and their very poor solubility in organic solvents are the most serious problems that control further advances in this very important field. Taka-hashi and coworkers have recently developed a synthetically useful method for preparation of fused aromatic compounds, by using the zirconocene-mediated aromatization of alkynes. In order to solve the solubility problem, alkyl substituents are introduced into to the skeletons. In principle, two types of synthetic protocols have been used. Type I protocol is via the homologation starting from a functionalized benzene derivative (Scheme 3) [75] the Type II protocol is via the intermolecular cycloaddition of two alkynes to an arene (Scheme 4) [76]. 

Aryl- and alkenylcarbene complexes are known to react with alkynes through a [3C+2S+1C0] cycloaddition reaction to produce benzannulated compounds. This reaction, known as the Dotz reaction , is widely reviewed in Chap. Chromium-Templated Benzannulation Reactions , p. 123 of this book. However, simple alkyl-substituted carbene complexes react with excess of an alkyne (or with diynes) to produce a different benzannulated product which incorporates in its structure two molecules of the alkyne, a carbon monoxide ligand and the carbene carbon [128]. As referred to before, this [2S+2SH-1C+1C0] cycloaddition reaction can be carried out with diyne derivatives, showing these reactions give better yields than the corresponding intermolecular version (Scheme 80). 

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