Hexenes cycloaddition with

In addition, phenylsufonylallene (110), a,(3-unsaturated phosphonates (111), and alkenes with perfluorinated substituents (112) are all useful dipolarophiles. The yields observed with methyl 2-propenoate are significantly lower than those with the corresponding acrylate (entries 7 and 9), because of the additional substituent. On the other hand, the dipolar cycloadditions with either ethyl vinyl ether, 1-hexene, cyclohexene, or a trisubstituted dipolarophile provide the corresponding isoxazolidines in either low yields or not at all (18). 

Isolable sterically congested cyclobutadienes react with electrophilic alkenes under mild conditions. tert-Butyl 2,3,4-tri-tert-butylcyclobutadienecarboxylate undergoes cycloadditions with both tetracyanoethene17 and maleic anhydride1S at — 20 to — 30 °C to give the correspondingly substituted bicyclo[2.2.0]hexenes. 

Nonetheless, there are a small number of systems that do mediate such [2 -i- 2 -t- 2] cycloadditions. With allenes as the alkene , cycloaddition with both acetylene and terminal alkynes proceeds regio-selectively to give 3,5-dimethylenecyclohexenes using Ni catalysts, and mostly 3,6-dimethylenecyclo-hexenes using Ni° catalyst precursors (equation 19). Norbomadiene undergoes so-called homo-Diels-Alder cycloaddition with both alkenes and a ynes in the presence of nickel catalysts. Further elaboration of this chemistry with alkynes but not alkenes has been described using a Co/Al catalyst system (equation 20). Attempts to produce cyclohexenes via all-intramolecular [2 + 2 + 2] cycloaddition of l,13-dien-7-ynes or 1,1 l-dien-6-ynes have been unsuccessful. ... 

The cycloaddition reaction of compound 6 with N-aryl- and N-aralkylazides 23 was also investigated (967(52)7183). Thiadiazabicyclo[3.1.0]hexene derivatives 25 were obtained from the labile triazoline intermediate 24 through nitrogen elimination. This bicyclic system underwent thermal transformation, producing thiadiazine dioxides 26 as the main product together with thiazete dioxides 27 and pyrazoles 28. 

Cycloalkene Derivatives Cyclopropenes readily interact with nitrile oxides. Reactions of a broad series of 3,3-disubstituted cyclopropenes with 4-substituted benzonitrile, methoxycarbonyl- and cyanoformonitrile oxides (229) as well as with di(isopropoxy)phosphorylformonitrile oxide (230) give 2-oxa-3-azabicyclo[3.1.0]hexene derivatives 62. Stereoselectivity of the cycloaddition is governed by both steric and polar factors. In particular, steric factors are supposed to prevail for 3-methyl-3-phenylcyclopropene affording 62 [R1 =... 

Harwood and Lilley (87) reported the tandem generation and intramolecular trapping of a stabilized azomethine ylide, derived from the enantiopure template examined in detail in Section 3.2.3. Condensation of 5-hexenal with template 205 under standard conditions led to in situ ylide generation and subsequent cycloaddition of the tethered alkene to furnish 296 as a single enantiomer in 95% yield after purification and this despite the fact that the dipolarophile is unactivated. Hydro-genolytic destruction of the template revealed the bicyclic amino acid 297 in 75% yield (Scheme 3.97). 

Cycloaddition is the most common source of 1,2-oxazetidine skeletons, but sometimes it is also useful to construct 1,3-oxazetidine rings. Indeed, in contrast to the usual reactivity exhibited by mtinchnones, which react with multiple bond systems as azomethine ylides by a [3+2] cycloaddition process, azete 58 was found to react with miinchnone 59, under thermal conditions, to give an isomeric mixture of the oxazabicyclo[2.2.0]hexene (E/Z)-26,... 

Competition between C=0 and C=C was observed in diphenylketene from which a lactone and a ketene acetal were obtained with the ylide of dimedone [23]. A different type of cycloaddition occurred with PhI=C(C02Me)2 this reacted catalytically with several alkenes (1-hexene, styrene, methyl methacrylate, etc.) with formation of lactones [24] ... 

Dipolar cycloadditions between nitrilimines 37, obtained in situ from 36, and alkenyl dipolarophiles 38 afford a mixture of pyrazoles 39 and 41 and tetrazines 40. Tetrazine byproducts 40 were obtained in good yields using 1-hexene as dipolarophile, Cs2C03 as base and with aryl as p-tolyl (50%) or as p-Br-phenyl (67%) <02NJC1340>. 

Simple olefins undergo cycloaddition, one way or another, in the metathesis process with remarkable ease e.g., with a tungsten halide catalyst at room temperature, 2-pentene is converted to an equilibrium mixture of 2-butene, 2-pentene and 3-hexene in a few seconds >. One should reasonably expect a similar transformation of simple acetylenes, e.g., 26 - -27. The transformation 26 27 might appear, at first inspection, to be symmetry-allowed. 

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