Isomerisation fragment

In the olivanic acid series of carbapenems the ( )-acetamidoethenyl grouping can be isomerised to the (Z)-isomer (19) (22) and reaction with hypobromous acid provides a bromohydrin that fragments to give a thiol of type (20) when R = H, SO H, or COCH. The thiol is not isolated but can react to provide new alkyl or alkenyl C-2 substituents (28). In the case of the nonsulfated olivanic acids, inversion of the stereochemistry at the 8(3)-hydroxyl group by way of a Mitsunobu reaction affords an entry to the 8(R)-thienamycin series (29). An alternative method for introducing new sulfur substituents makes use of a displacement reaction of a carbapenem (3)-oxide with a thiol (30). Microbial deacylation of the acylamino group in PS-5 (5) has... 

The oligomerisation of isobutene, with and without isomerisation or fragmentation, and its polymerisation and co-polymerisation are industrial processes of considerable... 

In the chemical and petroleum industries, the term cracking is used to describe a chemically complex process in which the decomposition of larger hydrocarbon molecules into smaller fragments plays a dominant role but is accompanied by a number of other reactions (isomerisation, cyclisation, polymerisation, disproportionation etc.). In this section, under catalytic cracking, only the primary fission of a C—C bond, which yields an alkene and a fragment with a C—H bond in the place of the former C—C bond... 

HPLC H NMR spectroscopy using an isocratic separation with acetonitrile and D2O in the ratio 7 13 has also been used to study photo-isomerisation of the natural material azadirachtin extracted from the seeds of the neem tree and which is a powerful insect anti-feedant [34], This has a complex structure with an (ii)-2-methylbutyl-2-enoate fragment but which after exposure to UY iradiation is converted to the Z-isomer ... 

Fig. 16 Thermal isomerisation of the photoisomer 33pJoto and the photochemical back reaction. The pyridine ligand moves from an external position to an intra-ring location while the - (CH2)i8 - fragment undergoes a folding/unfolding process...

The first and simplest labelling study is merely to have the metal fragment at vertex 3 in the (transient) overcrowded metallacarborane. Following route b+e one predicts one isomer of the C2" intermediate in which the heteroatoms (M and C) are in the same positions actually determined for (3). Thereafter route f+k+i predicts (one isomer of) an isomerised icosahedron (5), observed as compound (4), whilst route j+i would predict (one isomer of) an alternative icosahedron (6), not observed. 

Volume 9 deals with the majority of addition and elimination reactions involving aliphatic compounds. Chapter 1 covers electrophilic addition processes, mainly of water, acids and halogens to olefins and acetylenes, and Chapter 2 the addition of unsaturated compounds to each other (the Diels-Alder reaction and other cycloadditions). This is followed by a full discussion of a-, y- and S-eliminations (mainly olefin and alkyne forming) and fragmentation reactions. In Chapter 4 carbene and carbenoid reactions, and in Chapter 5 alkene isomerisation (including prototropic and anionotropic, and Cope and Claisen rearrangements), are discussed. 

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