O- carbonate

Tin enolates of ketones can be generated by the reaction of the enol acetate 733 with tributyltin methoxide[60i] and they react with alkenyl halides via transmetallation to give 734. This reaction offers a useful method for the introduction of an aryl or alkenyl group at the o-carbon of ketones[602]. Tin enolates are also generated by the reaction of siiyl enol ethers with tributyltin fluoride and used for coupling with halides[603]. 

Electronically, we find that strongly polarized acyl compounds react more readily than less polar ones. Thus, acid chlorides are the most reactive because the electronegative chlorine atom withdraws electrons from the carbonyl carbon, whereas amides are the least reactive. Although subtle, electrostatic potential maps of various carboxylic add derivatives indicate the differences by the relative blueness on the C-O carbons. Acyl phosphates are hard to place on this scale because they are not used in the laboratory, but in biological systems they appear to be somewhat more reactive than thioesters. 

The Curtius rearrangement, like the Hofmann rearrangement, involve migration of an -R group from the G-O carbon atom to the neighboring nitro gen with simultaneous loss of a leaving group. The reaction takes place on heat ing an acyl azide that is itself prepared by nucleophilic acyl substitution of m acid chloride. 

Fig. 1. Schematic representation of the chain alignment of a triple helix. Circles represent o-carbons, that of glycine is denoted number 1. Heavy circles indicate the chain in front, the N-terminal is at the bottom. The intrachain hydrogen bonds are designated by broken lines...

Fig. 31.— The Two Possible Conformations of Aspartame (18) Interacting with the Receptor Site." [Key O, carbon G, oxygen , nitrogen and o, hydrogen.]...

Bidentate NHC-Pd complexes have been tested as hydrogenation catalysts of cyclooctene under mild conditions (room temperature, 1 atm, ethanol). The complex 22 (Fig. 2.5), featuring abnormal carbene binding from the O carbon of the imidazole heterocycles, has stronger Pd-C jj, bonds and more nucleophilic metal centre than the bound normal carbene chelate 21. The different ligand properties are reflected in the superior activity of 22 in the hydrogenation of cyclooctene at 1-2 mol% loadings under mild conditions. The exact reasons for the reactivity difference in terms of elementary reaction steps are not clearly understood [19]. 

Allylic alkylations of cinnamyl carbonate by sodium malonate have been studied with a series of ruthenium catalysts, obtained from the azohum salts 126-128 and the ruthenium complex 129 (Scheme 2.25) in MeCN or THF to give moderate yields of mixtures of alkylated products in the allylic and ipi o-carbons (90 10 to 65 35). The observed regioselectivity is inferior to similar ruthenium systems with non-NHC co-ligands. The stereoelectronic factors which govern the observed regioselectivity were not apparent [102]. 

Benzo-fused pyridopyrrolizines can be prepared by an acid-induced cyclodehydration of the appropriately substituted hydroxypyrrolopyridines. In the case of 124 (Equation 7), this is best rationalized as an intramolecular electrophilic substitution at the o-carbon of the benzyl substituent <1988CC623, 1990J(P1)1757, 2001J(P1)1446>. 

Figure 12.1 Fatty acid carbon numbering system. The carbon atoms are numbered in sequence with the carboxyl carbon atom as number 1. By this system the terminal methyl carbon of oleic (octadecenoic) acid is number 18. An older system names this methyl carbon as the o-carbon and the adjacent carbon atom as number 2. Numbering then continues towards the carboxyl carbon and values are given for n to denote the number of carbon atoms from the o-carbon to any double bonds. See Table 12.3.

Based on older terminology where the numbering is from the o-carbon (the terminal methyl group) and n denotes the number of carbon atoms from the last double bond to the o-carbon. More acceptable nomenclature designates the carboxyl carbon as carbon 1. 

A protein, of course, is a polypeptide chain made up of amino acid residues linked together in a definite sequence. Amino acids are handed (except for glycine, in which the normally asymmetric o-carbon has two hydrogens), and naturally occurring proteins contain only L-amino acids. That handedness has far-reaching effects on protein structure, as we shall see, and it is very useful to be able to distin-... 

CK 3 carbon black, CK 3, manufactured by Degussa, Frankfurt a.M., Germany. Philblack O carbon black, Philblack O, manufactured by Phillips Petroleum Co., Akron, Ohio. 

SEAL CHAMBER DATA (2.1.6Q.1.7) temperature (°C) PRESSURE (kPa) FLOW (m /h) n SEAL CHAMBER SIZE /TABLE 2.3) TUBING O CARBON STEEL PIPE STAINLESS STEEL PIPINGASSEMBLY (3.5.2.10.1) THREADED O UNIONS SOCKET WELDED FLANGED TUBE TYPE FITTINGS PRESSURE SWITCH /PLAN 52/53) TYPE... 

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