Olefins heterocyclic synthesis

Dipolar cycloaddition of azides with olefins provides a convenient access to triazolines, cyclic imines, and aziridines and hence is a valuable technique in heterocyclic synthesis. For instance, tricyclic -lactams 273 - 276 have been synthesized using the intramolecular azide-olefin cycloaddition (lAOC) methodology (Scheme 30) [71]. 

Intramolecular addition of vinyl radicals to olefins as a method for heterocycle synthesis has been examined. The vinyl radicals can be conveniently generated from vinyl bromides and samarium(II) diiodide [95JOC7424], The intermediate radical after cyclization undergoes a further electron transfer from samarium to furnish a carbanion which is quenched at the end of the reaction. A samarium(II) diiodide mediated aryl radical cyclization onto a dihydrofuran has been reported [95T8555],... 

Aminochromes, 5, 205 Aminomethylenemalonates and their use in heterocyclic synthesis, 54 4-Amino-1,2,3-triazoles, 40, 129 Anils, olefin synthesis with, 23, 171 Anionic cr-adducts of heterocycles, 34, 305 Anions, ring-opening of five-membered heteroaromatic, 41, 41 Annelation of a pyrimidine ring to an existing ring, 32, 1... 

Among particular olefins recently synthesized is tetra-acetylethylene (277), potentially useful for heterocyclic synthesis. ... 

RCM reaction had major impact in the field of medium ring-sized heterocycle synthesis as demonstrated by numerous publications in this area [60,61]. However, the reaction also suffers from many of the drawbacks of common organic transformations, and thus has drawn attention for greener applications. Grubbs and coworkers developed a highly active water-soluble olefin metathesis catalyst of the type 99 (Figure 5) for this purpose [62]. 

The problem of the synthesis of highly substituted olefins from ketones according to this principle was solved by D.H.R. Barton. The ketones are first connected to azines by hydrazine and secondly treated with hydrogen sulfide to yield 1,3,4-thiadiazolidines. In this heterocycle the substituents of the prospective olefin are too far from each other to produce problems. Mild oxidation of the hydrazine nitrogens produces d -l,3,4-thiadiazolines. The decisive step of carbon-carbon bond formation is achieved in a thermal reaction a nitrogen molecule is cleaved off and the biradical formed recombines immediately since its two reactive centers are hold together by the sulfur atom. The thiirane (episulfide) can be finally desulfurized by phosphines or phosphites, and the desired olefin is formed. With very large substituents the 1,3,4-thiadiazolidines do not form with hydrazine. In such cases, however, direct thiadiazoline formation from thiones and diazo compounds is often possible, or a thermal reaction between alkylideneazinophosphoranes and thiones may be successful (D.H.R. Barton, 1972, 1974, 1975). 

Synthesis of the title compound is representative of a number of syntheses of nonaromatic nitrogen heterocycles via Pd(Ill-catalyzed amination of olefins. These tosylated enamines are not readily available by standard synthetic methods, and show potential for further functionalization of the heterocycle. The saturated amine can be synthesized from the title compound by hydrogenation of the double bond followed by photolytic deprotection. ... 

Synthesis of heterocycles, among them macroheterocycles, using olefin metathesis 98T4413. 

Bicychc pyrazinones foimd in several natural products were synthesized via Michael addition of heterocyclic amines to nitro olefin followed by reduction/cyclization of the nitro group of the adduct [20] (Scheme 5). Further elaboration of the C-6 methoxycarbonyl group in pyrazinone to the n-propyl guanidine group could result in the synthesis of indoloperamine. 

In the synthesis of N heterocycles, this technique also overcomes competitive retro Michael addition that lowers the yield of 1,4-adduct in the Michael addition of amines to nitro olefins. Thus, a toluene solution of nitro olefin 159 was treated with allylamine 160, EtgN, and TMSCI under nitrogen at ambient tern-... 

For further dehydration, for example, of aldoximes and amides to nitriles, of alcohols to olefines, as well as the synthesis of heterocycles like oxiranes and aziridines see Section 18.5. 

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