Side chain decomposition

The mold metabolite mycelianamide, isolated from the mycelium of strains of Penicillium gritieofulvum Dierckx, was first investigated by Oxford and Raistrick. The reinterpretation and extension of this work by Birch et and the revision by Bates et of the structure first proposed for the terpenoid side-chain, have led to the formulation of mycelianamide as 11. This structure has been confirmed by further degradations and by a synthesis of racemic deoxymyceli-anamide by Gallina and co-workers. The ready decomposition of the heterocyclic ring by either acid or alkali is discussed later (Section... 

The lower thermal stability of cardanol-formaldehyde resin and their derivatives were expected because of the presence of the libile side chain in the system. Although phenolics are superior in their properties, their bromo derivatives exhibit very low char yields. Oxidation of the char by a decomposition product is suspected. Evaluation of the LOI data with char yields individually for phosphorus and bromine suggests a positive interac-... 

The strained bicyclic carbapenem framework of thienamycin is the host of three contiguous stereocenters and several heteroatoms (Scheme 1). Removal of the cysteamine side chain affixed to C-2 furnishes /J-keto ester 2 as a possible precursor. The intermolecular attack upon the keto function in 2 by a suitable thiol nucleophile could result in the formation of the natural product after dehydration of the initial tetrahedral adduct. In a most interesting and productive retrosynthetic maneuver, intermediate 2 could be traced in one step to a-diazo keto ester 4. It is important to recognize that diazo compounds, such as 4, are viable precursors to electron-deficient carbenes. In the synthetic direction, transition metal catalyzed decomposition of diazo keto ester 4 could conceivably furnish electron-deficient carbene 3 the intermediacy of 3 is expected to be brief, for it should readily insert into the proximal N-H bond to... 

Unfortunately, complexes 39 and 40 are still more prone to decomposition than catalyst 16. Therefore, Grubbs sought to investigate a series of new ruthenium catalysts bearing NHCs with varying degrees of iV-heterocyclic backbone and aryl side chain substitution, and catalysts 16 and 30a were chosen as basic catalyst structures [57]. In 2009, complexes 41a-c and 42a-c were prepared to attempt to understand how the degree of substitution on the backbone influences catalyst activity and lifetime (Fig. 3.15). 

An interesting feature of 5-tocopherylacetic acid (51) and its derivatives was their appreciable thermal stability up to 200 °C. In contrast to 5a-substituted tocopherols carrying an electronegative substituent at C-5a, the homopolar C—C bond in the C2-unit at the 5-position of the tocopherol skeleton was shown to be very stable. Thermal decomposition of 51 at temperatures above 250 ° C caused a complete breakdown of the chroman structure, the C3-unit consisting of C-2, C-2a, and C-3 being eliminated as propyne, the side chain as 4,8,12-trimethyltridec-l-ene (Fig. 6.38). Fragmentation... 

The distinction between Pd and Rh catalysts was also verified for diazoketone 190. In this case, the carbonyl ylide was trapped by intramolecular [3+2] cycloaddition to the C=C bond195. Decomposition of bis-diazoketone 191 in the presence of CuCl P(OEt)3 or Rh2(OAc)4 led to the pentacyclic ketone 192 most remarkably, one diazoketone unit reacted by cyclopropanation, the second one by carbonyl ylide formation 194). With [(r 3-C3H5)PdCl]2, a non-separable mixture containing mostly polymers was obtained, although bis-diazoketones with one or two allyl side chains instead of the butenyl groups underwent successful twofold cyclopropanation 196). 

Investigation of the thermal decomposition of the novel architectures of POSS macromonomers and POSS siloxane co-polymers was reported.598 Novel, thermally stable polysiloxanes with bulky side-chain tris(trimethylsilyl)hexyl, and reactive glycidoxypropyl substituents, were recently described.599... 

A second method of activating the acid for esterification (see Section 7.6) is as the mixed anhydride. The mixed-anhydride reaction had been employed decades ago for preparing activated esters. However, it was never adopted because of its unreliability and the modest yields obtained. The method was fine-tuned (Figure 7.12), after reliable information on the properties of mixed anhydrides was acquired (see Section 2.8). Tertiary amine is required for esterification of the mixed anhydride to occur. The method is generally applicable, except for derivatives of asparagine, glutamine, and serine with unprotected side chains. The base also prevents decomposition that occurs when the activated derivative is a Boc-amino acid (see... 

There are six main decomposition pathways for protonated DKPs and elimination of one of the amino acid side chains or produces an ion which is the origin of five other fragmentation pathways. Owing to the symmetric structure of the DKP ring with regard to R and R, only half of the fragment ions are shown in Figure 3. ... 

Chlorpyrifos is stable to hydrolysis in the pH range of 5-6 (Mortland and Raman, 1967). However, in the presence of a Cu(lf) salt (i.e., cupric chloride) or when present as the exchangeable Cu(II) cation in montmorillonite clays, chlorpyrifos is completely hydrolyzed via first-order kinetics in <24 h at 20 °C. It was suggested that chlorpyrifos decomposition in the presence of Cu(II) was a result of coordination of molecules to the copper atom with subsequent cleavage of the side chain containing the phosphorus atom forming 3,5,6-trichloro-2-pyridinol and 0,0-ethyl-0-phosphorothioate (Mortland and Raman, 1967). 

---