Simple Cleavage

Both cis- and rrans-l-arylsulfonyl-2-arylsulfenyl propenes (56) underwent a Smiles rearrangement under electron impact at 20 and 70 eV and formed a diarylsulfide ion [M — 104]+ (equation 27a)39 through a process where a bond between the R C H group and the sulfide sulfur is formed and a rearomatization occurs by a loss of the neutral thiirene dioxide or a simultaneous expulsion of SOz and propyne. The ion m/z 148 was also obtained from all of the sulfonyl-sulfides, 56 (equation 27b) and here the loss of R2 seemed to be related to the bond strength39. In addition to the above compounds 56 exhibited some simple cleavages before and after sulfone-sulfinate rearrangements. 

Category 1, Simple Cleavage into Radicals.Aldehydes and ketones absorb in the 230-330-nm region. This is assumed to result from an n—>tt singlet-singlet transition. The excited aldehyde or ketone can then cleave. ... 

Two competing reactions are the homodienyl [1,5] shift (if a suitable H is available, see 18-29), and simple cleavage of the cyclopropane ring, leading in this case to a diene (see 18-3). 

Stevenson s Rule (Stevenson-Audier). A simple cleavage of a chemical bond in an odd electron ion may result in two pairs of ions and neutrals ... 

When all the available information is extracted from the molecular ion cluster it is possible to pass to the fragment ions. As mentioned above the fragment ions arise due to simple cleavages of the chemical bonds and to rearrangements. For the interpretation... 

We have reported that ESR and ENDOR (52) examination of degassed, irradiated samples of a number of polymers (PDHS, PDBS, poly(di-a-tetra-decylsilane) (PDTDS), poly(di-n-octylsilane (PDOS), poly(di-n-decylsilane) (PDDS) and poly(di-4-methylpentylsilane) (PDMPS) shows the formation of radical species which are persistent for hours and even days. The radical spectra (see Figure 4) are, however, clearly not consistent with those expected from the simple cleavage of the polymer backbone as described by Equation [2]. The structure of these radicals... 

The simple cleavage of lactones 1 or 2 with alcohol and acid has not been reported. However, when 1 is treated with benzaldehyde diethyl acetal and hydrochloric acid, ethyl 3,5 4,6-di-0-benzylidene-L-gulonate (47) is formed in >90% yield.77,78 No other isomers were observed, and other acetals of benzaldehyde, as well as aliphatic aldehydes, afford similar products in good yield.77 D Addieco prepared36 similarly protected derivatives of L-gulonic acid by oxidation of l,3 2,4-di-0-ethylidene-D-glucitol (15), followed by esterification of the resulting acid with diazomethane. 

Nitro compounds may show two different simple cleavages with respect to the nitro functionality, i.e. cleavage of the C—N and N—O bond, respectively. 

Reduction of 2-bromo-3-pentanone at mercury affords a mixture of 3-pentanone and l-hydroxy-3-pentanone, whereas electrolysis of Q ,Q -dibromoacetone in the presence of benzoate gives a mixture of products arising from both a carbon-bromine bond cleavage and an Sn2 displacement of bromide by benzoate [94]. In an acetic acid-acetate buffer, branched dibromo ketones, such as 2,4-dibromo-2,4-dimethyl-3-pentanone, are reduced to a-acetoxy ketones however, less highly substituted compounds, such as 4,6-dibromo-5-nonanone, undergo simple cleavage of both carbon-bromine bonds [95]. Other work dealing with the reduction of Q, Q -dibromoketones has been described [96]. 

Ingemann, S. Hammerum, S. Derrick, P.J. Fokkens, R.H. Nibbering, N.M.M. Energy-Dependent Reversal of Secondary Isotope Effects on Simple Cleavage Reactions Tertiary Amine Radical Cations With Deuterium at Remote Positions. Org. Mass Spectrom. 1989, 24, 885-889. 

Example In the El mass spectrum of 3,3-dimethyl-2-butanone no fragment ion due to McLafferty rearrangement can be observed, because there is no y-hydrogen available (Fig. 6.23). Instead, the products are exclusively formed by simple cleavages as evident from their odd-numbered m/z values. The highly stable tert-butyl ion, m/z 57, predominates over the acylium ion at m/z 43 (Chap. 6.6.2). 

The RDA reaction is often observed from steroid molecular ions, and it can be very indicative of steroidal stmcture. [107,110,113,114] The extent of the RDA reaction depends on whether the central ring junction is cis or trans. The mass spectra of A -steroidal olefins, for example, showed a marked dependence upon the stereochemistry of the A/B ring juncture, in accordance with orbital symmetry rules for a thermal concerted process. In the trans isomer the RDA is much reduced as compared to the cis isomer. The effect was shown to increase at 12 eV, and as typical for a rearrangement, the RDA reaction became more pronounced, whereas simple cleavages almost vanished. This represented the first example of such apparent symmetry control in olefinic hydrocarbons. [114]. 

Organoarsenic and -arsenate compounds have been studied by Froyer and Moller (172-173). In the initial stages, (CH3CH20)sAs0 fragments by simple cleavage (6) (Scheme 2), after which the (RO)2AsO" ... 

A major advancement in the Fmoc-based solid-phase synthesis of Tyr(P)-peptides was realized with the Fmoc-Tyr[PO(OR1)2]-OH derivatives 7 (R1 = Bzl, tBu, Mdpse) [Mdpse = 2-(methyldiphenylsilyl)ethyl] in which the acid-labile phosphate esters offered simple cleavage by TFA treatment. While the initial difficult synthesis of derivatives 7 restricted general synthetic usage, the subsequent commercial availability of these derivatives and their compatibility with solid-phase synthesis has provided a simple and efficient procedure for the routine synthesis of large complex Tyr(P)-peptides. 

---