Dipolar Reactions

Matsumoto, Y. Sawada and T. Katsuki, Pure Appl. Chem., 2008, 80, 1071. 

Shimada, S. Kondo, Y. Ohara, K. Matsumoto and T. Katsuki, Synlett, 2007, 2445. 

Kumadaki and A. Ando, Chem. - Asian 2008, 3,1850. 

Methods and Applications of Cycloaddition Reactions in Organic Syntheses, ed. N. Nishiwaki, John Wiley sons, Hoboken, New Jersey, 2014. 

---

With NJV -thiocarbonyldi-1,2,4-triazole the corresponding ethyl-5-(l,2,4-triazol-l-yl)-l,2,3-thiadiazole-4-carboxylate was obtained in 90% yield.[ 1291 However, analogous 1,3-dipolar reactions in the presence of (C2H5)3N are reported to yield the isomeric 2-(l-imidazolyl)-1,3,4-thiadiazoles 130],[ 1311... 

In a recent study, classical heating, microwave radiation and gamma radiation have been compared as energy sources to perform 1,3-dipolar reactions between unsaturated oximes and conventional dipolarophiles. On using gamma radiation the reactions were clean and yields obtained were similar to those for the thermal reactions. However, microwave radiation reactions were extremely clean, occurred more rapidly and gave higher yields [102],... 

Diels-Alder reactions. In the last two sections, the asymmetric 1,3-dipolar reaction [2+3] and cyclopropanation reactions [1+2] are discussed. 

Dipolar addition is closely related to the Diels-Alder reaction, but allows the formation of five-membered adducts, including cyclopentane derivatives. Like Diels-Alder reactions, 1,3-dipolar cycloaddition involves [4+2] concerted reaction of a 1,3-dipolar species (the An component and a dipolar In component). Very often, condensation of chiral acrylates with nitrile oxides or nitrones gives only modest diastereoselectivity.82 1,3-Dipolar cycloaddition between nitrones and alkenes is most useful and convenient for the preparation of iso-xazolidine derivatives, which can then be readily converted to 1,3-amino alcohol equivalents under mild conditions.83 The low selectivity of the 1,3-dipolar reaction can be overcome to some extent by introducing a chiral auxiliary to the substrate. As shown in Scheme 5-51, the reaction of 169 with acryloyl chloride connects the chiral sultam to the acrylic acid substrate, and subsequent cycloaddition yields product 170 with a diastereoselectivity of 90 10.84... 

Kobayashi s chiral lanthanide complex 63 has been used for asymmetric Diels-Alder reactions, and very good results have been obtained (see Section 5.4.2). This kind of complex is also effective in asymmetric 1,3-dipolar reactions.87 The chiral ligand is prepared in situ by mixing Yb(OTf)3,... 

Bis(oxazoline)-type complexes, which have been found useful for asymmetric aldol reactions, Diels-Alder, and hetero Diels-Alder reactions can also be used for inducing 1,3-dipolar reactions. Chiral nickel complex 180, which can be prepared by reacting equimolar amounts of Ni(C10)4 6H20 and the corresponding (J ,J )-4,6-dibenzofurandiyl-2,2 -bis(4-phenyloxazoline) (DBFOX/Ph) in dichloromethane, can be used for highly endo-selective and enantioselective asymmetric nitrone cycloaddition. The presence of 4 A molecular sieves is essential to attain high selectivities.88 In the absence of molecular sieves, both the diastereoselectivity and enantioselectivity will be lower. Representative results are shown in Scheme 5-55. 

As a kind of special case, the asymmetric 1,3-dipolar reaction of nitrile oxides or nitrones constitutes one of the most useful and convenient methods for preparing isoxazolidine derivatives. 

The 1,3-dipolar reaction (13DPR), whether concerted or not, undoubtedly rivals Diels-Alder reactions in ubiquity as well as synthetic utility [69], and its synthetic potential is still far from being exhausted. Both inter- and intramolecular 1,3-dipolar cycloadditions represent an efficient method for the... 

The first chapter, High Pressure Synthesis of Heterocycles Related to Bioactive Molecules by Kiyoshi Matsumoto, presents a unique high-pressure synthetic methodology in heterocyclic chemistry. Basic principles and fruitful examples for pericyclic reactions, such as Diels-Alder reactions, 1,3-dipolar reactions, and also for ionic reactions, such as Sn and addition reactions, are discussed. The review will be of considerable interest to heterocyclic chemists and synthetic chemists. 

The related 4-alky l-5-a Iky limino-1,2,3,4-th iatria/olcs 58 are much less stable than the corresponding aryl derivatives 52 and 55, and liberate nitrogen and sulfur to give the carbodiimides 59 in low yields (Equation 5). In many cases heterocumulenes 59 participate in consequent masked 1,3-dipolar reactions (see Section 6.09.6.2) with a second equivalent of compound 58 leading to complex reaction mixtures and explaining the low yields <1978J(P1)1440>. 

The last results reported in this field are related to the 1,3-dipolar reactions of tert-butyl ( )-4,4-diethoxy-2-p-tolylsulfinylbut-2-enoate and (S5,Ss) and (R5,Ss) 5-ethoxy-3-p-tolylsulfinylfuranones (42a and 42b) with different nitrile oxides [ 167]. Acyclic sulfoxides react with benzonitrile, acetonitrile, and bromo-formonitrile oxides to yield isoxazoles resulting in desulfinylation from the adducts. Cyclic dipolarophiles afford bicyclic isoxazolines in their reactions with benzonitrile oxide. The reactivity of the double bond as a dipolarophile is strongly increased by the sulfinyl group. The regioselectivity of these reactions... 

Aldehyde azines 87 react with two equivalents of dimethyl acetylenedicarboxylate in a 1,3-dipolar reaction to give iV-allyl pyrazoles 88 in good yields (Scheme 48) <2002CJC1293>. 1,3-Dipolar cycloaddition of polymer-supported -silylnitrosoamides 89 with dimethyl acetylenedicarboxylate gives pyrazole derivatives 90 without the necessity for a separate cleavage operation (Scheme 49) <2000TL691>. 

Kavitha, K. Manoharan, M. Venuvanalingam, P. 1,3-Dipolar reactions involving corannulene How does its rim and spoke addition vary , J. Org. Chem. 2005, 70, 2528-2536. 

The activation of the trifluoromethyl substituent is strong enough to allow the 1,3-dipolar reaction to occur with trisubstituted dipolarophiles, provided a second electron-withdrawing substituent is present in the molecule (Table 11). Under similar conditions non-fluorinated analogs are unreactive (entry 3).The cycloaddition with ethyl trifluoroacctoacetate is a striking example (Table 11, entry 2) in this case, the dipolarophile reacts in its enolic form (Z-isomer). 

The 1,3-dipolar cycloaddition reaction [57] between alkene and nitrone [58] is an effective procedure for generating new chiral centers attached to heteroatoms. J0r-gensen et al. [59a] found that remarkably high endo selectivity was induced in the 1,3-dipolar reaction by use of a phenanthroline-coordinated Mg(II) catalyst prepared in the presence of I2 as a co-catalyst (Sch. 32). By reaction of 74, an alkene bearing a chiral oxazolidinone, with benzylidenephenylamine A -oxide 73 in the presence of the Mg(II)-phenanthroline catalyst (10 mol %), one of the four possible diastereomers of the isoxazolines 75 was formed exclusively in an almost quantitative yield. 

These fluorinated Dewar benzenes are also reactive as dipolarophiles in the 1,3-dipolar reactions 63). 

---