Azines, olefins from

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). 

The most common byproducts encountered in cyclopropanations with diazoalkanes as carbene precursors are azines and carbene dimers , i.e. symmetric olefins resulting from the reaction of the intermediate carbene complex with the diazoalkane. The formation of these byproducts can be supressed by keeping the concentration of diazoalkane in the reaction mixture as low as possible. For this purpose, the automated, slow addition of the diazoalkane to a mixture of catalyst and substrate (e.g. by means of a pump or a syringe motor) has proven to be a very valuable technique. 

Structure and reactivity of nitrozonium complexes of organic compounds including azines, crown ethers, and heterocyclic cations from NO+ and olefins or arenes 01UK241. 

CF3)2C(0-S02F)N]2 (5— 25%) (yields were variable and non-reproducible), Previous work on the formation of criss-cross cycloadducts (l,3- 2,4-addition) from hexafluoroacstone azine and electron-rich olefins has been extended. For example, the reaction of the azine with isobutene at ca. 70 "C (12—24 h) was shown to give initially a 1 1 adduct (91 %), which combined slowly (14 days) with isobutene at 20 "C to give the criss-cross adduct (75) quantitatively. The initial product was formulated as the Diels-Alder adduct (76), but others have shown unequivocally by JIT-ray structure analysis of crystalline material obtained in hi yield (85 %) (CFj)8 (CF3)s... 

Pyrolysis of hexafluoroacetone azine (88) in the presence of olefins gives l,l-di(trifluoromethyl)cyclopropanes non-stereospedfically. The reaction is not by direct formation of bistrifluoromethylcarbene from (88) and an inter-molecular radical mechanism is the most probable of the mechanisms considered. 

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