Other Reactions of Diazomethane with Heterocycles

Heterocycles with olefinic C=C double bonds are able to add diazornetliane to form pyrazolines, for example, maleic acid imide,  

The C-mcthylation of methyl pyran-2-one-5-carboxylate (96) to methyl 6-methylpyran-2-one-5-carboxylate (97) can be in- 

The reactions of diazomethane with heterocycles containing a ketonic grouping in the ring do not differ, in principle, from those of alicyclic ketones (see footnotes 3 and 177) ring expansion and the formation of epoxides compete. In general, ring expansion is the more important reaction for example, tetrahydropyran-4-one (99) is converted to l-oxacycloheptan-4-one (100) (60%) and 4,4 -epoxy-4-methyltetrahydropyran (101) (23%).  

The reaction with A -cyclohexylidenepyrrolidinium perchlorate (101a) is particularly interesting 2,2-pentamethylene-l,l-tetramethyl-eneaziridinium perchlorate (101b) is formed in 88% yield.  

The reactions of heterocyclic 1,2-dicarbonyl compounds with diazomethane, which were studied by Eistert and his co-workers in 

TV-arylmaleic acid imides (92)173 and aconic acid (93)174 react in this way. 

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Most reactions of diazomethane with these heterocyclic systems involve attack at other functional groups (for a review see ref. 1), such as in the 0- and iV -methylation of the hydroxy-pyridines and -quino-... 

Reactions of diazomethane with various a,(3-unsaturated ketones were described in [27, 28]. For instance, Mustafa and Freifel [27] showed that treatment of chalcones 5 with ethereal diazomethane under normal conditions affected addition to the double bond of the ketone, forming pyrazolines 6 (Scheme 2.2). Alternative directions leading to heterocycles 7 as well as to methylation of the hydroxyl group were not observed. Similar results were described in [28]. On the other hand, Aleksandrova et al. [29] reported the formation of 4-aryl-3-(2-furoyl)-2-pyrazolines 9 when furyl analogues of chalcones 8 react with diazomethane. 

The exocyclic C=S bond of 5-thioxo-2-thiazolines (203) can act as a dipolarophile towards several compounds. For instance, cycloaddition reactions have been reported with nitrilium betaines (204) to give heterocyclic spiro compounds <84HCA534>, with thiocarbonyl ylides (205) to give spirocyclic 1,3-dithiolanes <9IHCA1386>, and with 2-diazopropane (206) to give thiadiazoles <92HCA1825>. On the other hand, the reaction of (203) with diazomethane leads to a mixture of five products (Scheme 49) <93hcai715>. 

Reactions offluorinated dipoles. In recent years, much effort has been devoted to the preparation of tnfluoromethyl-substituted 1,3-dipoles with the goal of using them to introduce trifluoromethyl groups into five-membered nng heterocycles Fluorinated diazoalkanes were the first such 1,3-dipoles to be prepared and used in synthesis A number of reports of cycloadditions of mono- and bis(tnfluo-romethyl)diazomethane appeared prior to 1972 [9] Other types of fluonne-substi-tuted 1,3-dipoles were virtually unknown until only recently However, largely because of the efforts of Tanaka s group, a broad knowledge of the chemistry of tnfluoromethyl-substituted nitrile oxides, nitnle imines, nitnle ylides, and nitrones has been accumulated recently... 

Identification of the product(s) resulting from the reaction of heterocyclic compounds with diazomethane has been used in attempts to elucidate their tautomeric composition (for summaries, see references 7 and 41). This work was based on the assumption that if a compound which is capable of existing in both an —NH and an —OH form produced only the =NMe derivative when it w as treated with diazomethane, it existed entirely in the =NH form. On the other hand, formation of the —OMe derivative was interpreted to mean that a finite amount of the compound existed in the —OH form. In some cases the tautomer present in the solid state w as concluded to be different from that present in solution for example, 41 42 gave a higher proportion of the 3,4-dimethoxy derivative when ethereal diaz-... 

All the P-As and P=As bonded compounds are sensitive to hydrolysis and to oxidation by air. The reaction of Cp As=PMes with diazomethane adds a CH2 group across the double bond and yields the three-membered heterocyclic phosphaarsirane Cp AsCH2PMes. Sulfur and selenium add across the double bond to form three-membered heterocycles.Dimerization of Cp As=PCp produces two isomeric diphosphadiarsetanes, one containing the P-P-As-As and the other the P-As-P-As core. Photolysis of Cp As=PMes, Cp P=AsMes, and (2,4,6-r-Bu3C6H2)P=AsCp yields the diarsadiphosphacyclo-butanes. Metal complexes of several of the P=As compounds have been prepared and characterized. ... 

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