Extrusion ring expansion

On the other hand, small-ring alkenes such as diphenylcyclopropene derivatives (125) may serve as substrates for the preparation of six-membered heterocycles by way of the cycloaddition-extrusion-ring-expansion reaction. Thus, thd reaction of (9) with (125a) leads to formation of (127a) via the primary adduct (126), whereas the reaction of (9) with (125b) yields (127b) and the tricyclic derivative (128) (75JCS(P1)632). 

Cycloaddition-extrusion-ring expansion reactions of five-membered mesoionic oxazolones and thiazolones with 2,3-diphenylcyclopropenethione produced pyridine-4(l//)-thiones... 

The dipolar cycloaddition of sydnones (l,2,3-oxadiazolidin-5-one derivatives) (108) with benzocyclobutene (109) has been used to synthesize 3 f-2,3-benzodiazepines (110). This synthesis involves a cycloaddition-extrusion-ring-expansion sequence, and with other mesionic compounds, for example the thiazolium-4-olate (111), primary cydoadducts (112) were isolated (Scheme 13)... 

Dicyanomethylenediphenylcyclopropene and an equimolar amount of mesoionic 3-methyl-2,4-diphenylthiazol-5-one refluxed 8 hrs. in xylene -> product. Y 74%. F. e. s. H. Matsukubo and H. Kato, Soc. Perkin I 1975, 632 4H-l,4-thiazine 1,1-dioxides by cycloaddition-extrusion-ring expansion s. Chem. Lett. 1975, 1153. 

Ready extrusion of sulfur dioxide from fused thiirane dioxides is well known and was observed in the formation of pyrazoles from 19b and diazoalkanes6,179. A ring expansion... 

Ring expansion of the sulphonamide reaction199 (equation 144) demonstrates the ability of a ruptured sulphur-centred free radical to undergo 1,3-Fries type migration200 (equation 145). Sulphur dioxide extrusion may also provide a synthetic route to fi-lactams201 (equation 146). 

Initially, ring expansion by tellurium leads to a four-membered heterocycle (n = 1) intermolecular rearrangements produce additional tellurium-phosphorus hctcrocycles, which are ultimately converted by extrusion of tellurium to tetra-/-butylcyclotetra-phosphane1. 

Cyclopropanation of tricarbonyl(tropone)iron 18 via cycloaddition of diazomethane, diazoethane or diazopropane and thermal dinitrogen extrusion gave bicyclo[5.1.0]octadienone ( homotropone ) complexes which decomposed to form the free ligand 20 in high yield. When the same procedure was applied to the free ligand 16, a substituted cyclooctatrienone system 17 was obtained via ring expansion. 

The same rearrangement pattern is obtained when chlorine instead of bromine is at the bridgehead as well as with the bicyclo[5.1.0] and [6.1.0] skeletons, but not with the [3.1.0] skeleton. 1,2-Hydride shifts can occur simultaneously or subsequent to halide extrusion. Thermolysis of 13 gave 3-chloromethylene-2-methylchroman-4-one 14. This product contrasts what that obtained on solvolysis of the 2-phenyl analog of 13 which occurs with ring expansion to yield a benzoxepine derivative (Section 2.4.1.3.1.1.2.). 

Further examples including extrusion and ring expansion reactions <75JCS(Pi)632> as well as intramolecular [3 -I- 2] cycloadditions have been reported <81LA347>. In addition, the mesoionic 1,3-dithiolones (124) react with formaldehyde regiospecifically in a [3 -i- 2] cycloaddition reaction with formation of the 2-oxa-6,7-dithiabicyclo[2.2.1]heptanone derivative (125) (Equation (17)) <78CB3l7l>. Furthermore, upon reaction with the N=N bond of dimethyl azodicarboxylate, (126) is obtained (Equation (18)) <78CB3171>. 

A new type of rearrangement is described by Rees and Yelland186,187 the 1-aminopyridone 60 when oxidized with lead tetraacetate gives the pyridazine 61 as the main product and a small amount of 62 and 63. It is supposed that the reaction proceeds via a nitrene, followed by ring expansion, valence isomerization, and extrusion of carbon monoxide. 

Pyrazine (V-ethoxycarbonylimines, when irradiated in acetone, afford pyrazoles 132 and the parent pyrazines.246 The formation of 132 may involve initial ring expansion to the 1,2,5-triazepines via the diaziridine intermediates. The triazepines may then isomerize to the bicyclic valence isomers, followed by extrusion of RCN to produce 132 (Eq. 44). 

Exhaustive dehydrogenation, 139-140, 338 Expansion of rings. See Ring expansion Extrusion of carbon dioxide, 80 of carbon monoxide, 78, 330 of molecular nitrogen, 35, 331, 334 of sulfur, 35, 38-39, 59-60, 80, 261, 334, 338 of sulfur dioxide, 80... 

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