CUMULATIVE systems

Nuclear Plant Reliability Data System Annual Reports of Cumulative System and Component Reliability for Period from July 1, 1974, through December 31, 1982, NPRD A02/A03 (INPO 83-034), Institute of Nuclear Power Operations, Atlanta, GA, October 1983. 

The dipyrrylacelylenedicarbaldehyde 18, which already contains, along with the acetylene moiety, two of the two-carbon bridges of the final macrotetracycle, can be prepared by a Heck-type coupling of 5-iodopyrrole-2-carbaldehydes with acetylene.8a,b The main conjugation pathway with 22n electrons is already present in the acetylene-cumulate systems 19. The expected planarity of this chromophore has been confirmed by X-ray structure analysis.8a b... 

Also of interest are the cumulative systems of sulfines and of carbon disulfide which react with nitrile oxides to give 5H-1,4,2-oxathiazole S-oxide (220) <77JCS(P1)1468> and 1,4,2-oxathiazol-5-one derivatives (221), respectively <66JOC24l7>. The latter is formed from the primary spiro bis adduct (222) by further decomposition (see also Section 4.14.5.6). 

The structure of ketene imine 188 was elucidated by means of a single-crystal X-ray diffraction analysis. Surprisingly, bond lengths of 133 and 120 pm for the cumulated system (C=C=N) hardly deviate from those found in a linear analogue (i.e., diphenylketene p-toluylimine) (193). Apparently, the cumulated bond system of 188 is not linear but rather is bent to an angle of 163.8°. 

However, from elegant labelling studies by Wentrup and coworkers on the gas-phase thermal interconversion of phenylnitrene and 2-pyridylcarbene, it became evident that an alternative and equally viable intermediate in these nitrene ring expansions is the azacycloheptatrienylidene (216) or its tautomer, the cumulated system (217) (81AHC(28)23l). 

Chapman and coworkers (79RTC334) from studies on the low temperature photolysis of phenyl azide in an argon matrix at 8 K produced convincing IR spectroscopic evidence for the formation of l-aza-l,2,4,6-cycloheptatetraene (217), rather than a benzazirine intermediate. In fact, these workers have reinterpreted the formation of 2-alkylamino-3ff-azepines on the basis of amine addition to the cumulated system (217) rather than the benzazirine. 

The problem, however, is not yet settled as contemporary studies on the photolysis of bicyclic azides, e.g. 1-naphthylazide, in an argon matrix at 12 K demonstrate clearly the existence of two transient species, the IR spectra of which correspond in one case to the cumulated system analogous to (217) and in the other, which absorbs strongly at 1708-1736 cm-1, to the azirine structure (218) (80CC499). 

It is of interest to note that a cumulated system rather than a benzazirine was suggested by Sato (68BCJ2524) to explain the photoinduced ring expansion of the azidocyclohexenone (219) in aqueous THF to the azepinedione (220 Scheme 23). Better yields of the dione have since been obtained by irradiating the azide in wet benzene (72CPB871). 

As for the multiply bonded systems of heavier group 14 elements, all the homonuclear double bonds were successfully isolated and characterized by the end of the last century. However, the chemistry of heteronuclear double bonds and those of conjugated systems are still in growth. The synthesis and isolation of unprecedented cumulative systems such as 217 and aromatic systems containing Ge, Sn and Pb atoms, e.g. 219-222 (Scheme 68), will also be within the range of this future chemistry. Likewise, the synthesis and isolation of the triply bonded systems 223 (Scheme 68) should be one of the most challenging projects in this field. 

Also, carbodiimides with a C=N bond in conjugation to the cumulative system undergo [2-1-4] cycloaddition reactions with suitable dienophiles (see Section 5.3.1). 

Conjugated n Electron and Cumulative Systems of Heavier Group 14 Elements 24... 

CONJUGATED ir ELECTRON AND CUMULATIVE SYSTEMS OF HEAVIER GROUP 14 ELEMENTS... 

The title reactions are discussed in a series of reviews . However, the most complete and detailed description of rearrangements involving allenes was presented in Huntsman s comprehensive survey, wherein the cumulated systems were considered as either the starting materials, the intermediates or the reaction products. More recently, very detailed reviews devoted to vinyl cations and containing numerous examples of rearrangements of cumulenes and other polyenes were published . Therefore, this section will cover only relatively recent publications. 

As fdr as conjugated and cumulated systems are concerned, it has been generally found that the ease of polymerization increases with the amount of unsaturation and that conjugation or cumulation of double bonds increases their reactivity. To support this general rule. Table 15-2 shows a comparison of the rates of polymerization of hydrocarbons that differ only in their unsaturation. 

Many carbenes add to cumulated systems, that is, allenes, to give alkyHdenecy-clopropanes in a synthetically useful reaction. Thus, allene itself reacts with ethoxycarbonylcarbene to give the ethyl ester of 2-methylenecyclopropane-l-carboxylic acid. 3-Methylbuta-l,2-diene (dimethylallene) has been proposed as a useful probe for carbene multiplicity since singlets add to the more substituted double bond, whereas triplets add to the 1,2-bond (Scheme 5.38). Carbenes react with enamines in the normal way accompanied by a ring expansion that generates ketones via rearrangement of the initially formed aminocyclopropane (Scheme 5.39). 

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