Twofold extrusion

Twofold extrusion from certain cyclic molecules... 

Thermolysis of diferrocenyltellone,250 as well as its reaction with M(CO)6 (M=Cr, Mo, W),221 yields the tetraferrocenylethylene by a twofold extrusion process from a preformed cyclic dimer of diferrocenyltelluroketone (Scheme 45). 

Elimination of CO2 from 21 requires higher temperatures. Reported protocols include the thermolysis without solvent at 130 °C (44), heating in solution at 150-230 °C (45), as well as in the gas phase at 600 °C (FVP) (46). For synthetic purposes, this method has been used for the preparation of sterically hindered olefins and represents an extension of the twofold extrusion methodology [cf. (47,48)]. 

As mentioned on pages 317 and 324, the 1,3-dipolar electrocycUzation of thiocarbonyl ylides leads to thiirane derivatives, which represents an excellent method for the preparation of those three-membered rings. Typically, thiiranes are isolated as the final products, but in some instances they are produced as intermediate compounds which spontaneously desulfurize to give alkenes [twofold extrusion (47,48)]. 

Olefin Synthesis by Twofold Extrusion Carbon dioxide,thio-extrusion... 

The above-mentioned twofold extrusion reaction proved to be particularly useful in the preparations of unsymme-trical 1,8-diazafluorenylidene derivatives such as 80 and 81 (Equation 32) <2003OBC2755>. In the case of sulfur and selenium, the alkenes were isolated directly in good yield. In the tellurium reaction, a mixture of the alkene and thiirane was obtained and could be desulfurized to the desired alkene 81 with triphenylphosphine in refluxing benzene (Equation 33). 

The twofold extrusion of nitrogen and sulfur and selenium and sulfur from 1-thia- and l-selena-3,4-diazolines(77), readily available from the reaction of diazoalkanes with thio- and selenaketones, respectively, as well as from the reductive coupling of carbonyl compounds such as 78, is the preferred method for preparation of olefins of type I and II (98,99). Examples of the extrusion method, developed by Barton (100), and the McMurry reaction (101) are given in Scheme 1. 

T ris( diethy lamino)phosphine Ethylene derivs. by twofold extrusion... 

Several convenient olefin syntheses have been reported. N-Carbalkoxysulfamate esters undergo elimination to olefins at room temperature. Epoxides afford olefins by reductive elimination under the influence of MgBr2 and magnesium amalgam. A twofold extrusion process for the construction of complex olefins has also been described. In the example shown, the highly hindered olefin shown was obtained in 80% yield. 

The S-oxides (139) are readily oxidized to the sulphones (140), which are in turn pyrolysed with loss of sulphur dioxide as shown. This twofold extrusion-process confirms the sites of bond-formation in the original cycloaddition. ... 

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