Miscellaneous Cycloadditions

The influence of water as a solvent on the rate of dipolar cycloadditions has been reported [76]. Thus the rate of the 1,3-dipolar cycloaddition of 2,6-dichloroben-zonitrile N-oxide with 2,5-dimethyl-p-benzoquinone in an ethanol/water mixture (60 40) is 14-fold that in chloroform [76b]. Furthermore the use of aqueous solvent facilitates the workup procedure owing to the low solubility of the cycloadduct [76b]. In water-rich solutions, acceleration should be even more important. Thus in water containing 1 mol% of l-cyclohexyl-2-pyrrolidinone an unprecedented increase in the rate of the 1,3-dipolar cycloaddition of phenyl azide to norbornene by a factor of 53 (relative to hexane) is observed [77]. Likewise, the 1,3-dipolar cycloaddition of C,Ar-diphenylnitrone with methyl acrylate is considerably faster in water than in benzene [78]. Similarly, azomethine ylides generated from sarcosine and aqueous formaldehyde can be trapped by dipola-rophiles such as N-ethylmaleimide to provide pyrrolidines in excellent yields 

Using a Zincke-Bradsher convergent strategy for the synthesis of the ABE tricyclic core of Manzamine A, Magnier and Langlois reported the use of aqueous conditions to achieve, in one pot, the preparation of a naphthylpyridi-nium salt intermediate which underwent an inverse electron demand heterocyclic Diels-Alder cycloaddition with either ethyl vinyl ether or (Z)-l-ethoxy- 

The most striking effect of water as a solvent in related cycloadditions was observed in the [4+3] cycloaddition of a,o -dibromo ketones with furan (or pen- 

In this chapter, the details of several types of Ir-complex-catalyzed cycloadditions have been summarized. Although, compared to other late transihon-metal com-plexes-such as those of Pd, Ni, Ru and Rh-the examples are few in number, some notable Ir-catalyzed cyclizations have recently been reported which cannot be achieved when uhlizing other metal catalysts. Until now it has not yet been possible to identify any dishnct explanation for the unique reachvity of iridium, and in parhcular its different reachvity compared to rhodium, which is located just above iridium in the Periodic Table of the elements. Nonetheless, many further developments of efficient and prachcal Ir-catalyzed cycloadditions are to be expected in the near future. 

2 Reppe, W., Schlichting, O., Klager, K. and Toepel, T. (1948) Justus Liebig s Annalen der Chemie, 560, 1-92. 

4 Khand, I.U., Knox, G.R., Pauson, P.L., Watts, W.E. and Foreman, M.l. (1973) Journal of the Chemical Society-Perkin Transactions, 1, 977-81. 

5 Recent selected reviews (a) Carmona, D., Lamata, M.P. and Oro, L.A. (2000) Coordination Chemistry Reviews, 200-202, 717-72  

7 Recent reviews (a) Yamamoto, Y. (2005) Current Organic Chemistry, 9, 503-9  

3-dipolar cycloaddition, also known as the Huisgen cycloaddition, classic reaction in organic chemistry consisting of the reaction of a dipolarophile with a 1,3-dipolar compound that allows the production of various 5-membered heterocycles. In particular, the 1,3-dipolar cycloaddition reaction of nitrones with dipolarophiles such as alkenes has received considerable attention in 

Oxa-Diels Alder reactions of a,p-unsaturated trifluoromethyl ketones 

In recent years, azomethine ylides have become one of the most investigated classes of 1,3-dipoles and, based on their cycloaddition chemistry, various 

Even though aza-p-lactams have attracted interest because of their biological activities, only limited progress has been reported with regard to the enantio-selective synthesis of this family of heterocycles. The Staudinger [2-1-2] cycloaddition of ketenes with imines is a versatile and efficient route to 

Cyclopropanes are useful building blocks for the synthesis of natural and synthetic products due to their unique structures and reactivities. They are also found as a basic structural unit in a wide range of biologically active compounds. As a result, the development of efficient methods for the asymmetric synthesis of cyclopropanes has attracted intensive research interest in recent years.In 2008, Cao et al. reported a novel domino cyclopropanation-Wittig 

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One other miscellaneous cycloaddition reaction has been reported. Arynes generated from anthranilic acids 205 have been found to undergo cycUzation with Barton esters 206 to afford polycycUc heterocydes 207 in moderate yields (Scheme 12.59) [109], with the reaction presumably proceeding through a radical pathway. 

Miscellanous Cycloadditions. The ylide (23a R = H or Me Y = SOjMe or PPhj) condenses with diphenylcyclopropenone to give a tetralone (723) and the ylide derived from (724) affords the a-pyrone (725). ... 

Miscellaneous Cycloadditions. Restricted Hartree-Fock calculations have predicted a transoid approach of reagents for polar [2 + 2]cycloadditions in contrast to the available experimental data. The nucleophilic 1,2-cycloadditions of cyclopropenones and cyclopropenthiones have been discussed (p. 52) and no other 1,2-cycloadditions have been recorded except for those at sites remote from the three membered ring s s, 3oo... 

Miscellaneous Cycloadditions A rhodium-catalyzed [3-I-2-I-1] cycloaddition of an yne-ene-vinylcyclopropane motif with CO was used for the synthesis of a-agarofiiran. This reaction can be seen as a homologous Pauson-Khand reaction and was found to be quite general, allowing the synthesis of diversely substituted cyclohexenones (Scheme 7.11) [18]. 

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