A-benzoyl substituted

As already briefly mentioned, easily the most obvious change regarding optical properties appears in the transition from the open-chain precursor polymers to the planarized PPP ladder polymers (LPPP). The primary single-stranded coupling product (a benzoyl-substituted polyphenylene) from a Suzuki-type polycondensation between an alkyl- or alkoxy-substituted 2,5-dibromo-1,4-dibenzoylbenzene derivative and 2,5-dihexyl-l,4-phenylenediboronic acid is colorless with an absorption maximum Amax of 264 nm [n-TT transition c = 39,000 L/(moI cm)l (19]. This absorption behavior supports the strongly twisted structure of the main PPP chain. The mutual distortion of the aromatic subunits reduces the conjugative interaction to a minimum, so that the typical electronic properties of a conjugated polymer are almost completely lost. 

The benzoin ethers (75, R-alkyl R H) and the ot-alkyl benzoin derivatives (75, R=H, alkyl R =alkyl) undergo a-scission with sufficient facility that it is not quenched by oxygen or conventional triplet quenchers.276 This means that the initiators might be used for UV-curing in air. Unfortunately, it does not mitigate the usual effects of air as an inhibitor (Section 5.3.2). The products of a-scission (Scheme 3.53) are a benzoyl radical (13) and an ( -substituted benzyl radical (76) both of which may, in principle, initiate polymerization, 76 2"... 

Usually, a-bromo-substituted arenes have been prepared through the reaction of arenes with bromine under ultraviolet irradiation. In the presence of benzoyl peroxide, N-bromosuccinimide can also be used for this purpose. 

We found that the reaction of arenes with a calculated amount of BTMA Br3 in refluxing benzene in the presence of AIBN gave a-bromo-substituted arenes in fairly good yields. In this method, it was found that AIBN was a more effective free radical initiator than benzoyl peroxide (Fig. 15) (ref. 22). 

Due to their stability and their easy formation, many examples of transition metal complexes containing benzoyl-substituted thiourea ligands have been described [59-62]. Most of them concern Ft species in which the thiourea ligands behave as monoanions and are bounded to the metal centre through the S and O atoms, forming a six-member ring system (Scheme 10). 

Thompson SK, Smith WW, Zhao B, Halbert SM, Tomaszek TA, Tew DG, Levy MA, Janson CA, DAlessio KJ, McQueney MS, Kurdyla J, Jones CS, DesJarlais RL, Abdel-Meguid SS, Veber DF. Structure-based design of cathepsin K inhibitors containing a benzyloxy-substituted benzoyl peptido-mimetic. J Med Chem 1998 41 3923-3927. 

The five-coordinate complexes Ir(CO)(PPh3)2L, where HL = /3-diketone, A-benzoyl-A-phenyl-hydroxylamine, salicylaldehyde, 8-hydroxyquinoline, 2-hydroxybenzophenone, 2-hydroxy-8-methoxybenzophenone, were prepared from [Ir(CO)(PPh3)2Cl].632 The resulting compounds all underwent oxidative addition reactions with Br2. Reaction of [(cod)2IrCl]2 with N-substituted 3-hydroxy-2-methyl-4-pyridine gives the bichelated complex (389). 33... 

Industrially important pigments typically show the following substitution pattern A represents an ethoxy group, B represents an acetylamino or a benzoyl-amino moiety, and X is a chlorine atom or an NHCOCH3 function. The commercially most important compound 115, however, is somewhat of an exception in that A and E or B represent the heterocyclic moiety, which formally results... 

In what was intended as another experimental probe to ascertain whether a concerted or stepwise mechanism was involved in substitution reactions of arenesulfonyl chlorides, Rogne (1975) measured the enthalpies of transfer from propanol to acetonitrile for the transition states, SAH, for the reaction of imidazole with (a) benzoyl chloride and (b) benzenesulfonyl chloride. He found that SAH was considerably more negative for the reaction involving the sulfonyl chloride than for the one involving benzoyl chloride. This means that the transition state for attack of imidazole on benzenesulfonyl chloride is considerably better solvated by acetonitrile relative to its solvation by propanol... 

D. F. (1998). Stmcture-based design of cathepsin K inhibitors containing a benzyloxy-substituted benzoyl peptidomimetic. /. Med. Chem. 41,3923-3927. 

The oxazolidine system proved a good protecting group with which to mask the ethanolamine moiety in the a-formylation and a-benzoylation of 558, and it could also be used as an aldehyde donor in the rearrangement, based on the ring-chain tautomeric character of 559, under acidic conditions to yield 3-(2-hydroxyethyl)-substituted 1,3-oxazin-4-ones 560 (Scheme 106) <1996JOC3358>. 

A -acylaziridines substituted with an electron-withdrawing group produce a 2,4-disubstituted oxazoline as the major product. Borontrifluoride etherate (BF3 OEt2) has also been used successfully for an Al-benzoyl, but not an N-acetyl-substituted aziridine (Scheme 8.58). ... 

Thermal decomposition of the benzoyl-substituted A -thiabenzenes 490a and 490b affords alkyl-rearranged 2-(4-bromophenyl)-3a,6a-dihydro-3,6,6a-trimethylthieno[3,2-3]furan 491a and 2-(4-bromophenyl)-3-ethyl-3a,6a-dihydro-6,6a-dimethylthieno[3,2-3]furan 491b (Scheme 61). A plausible mechanism for the formation of these products is also discussed <2001J(P1)2269>. 

Rhodium acetylacetonate differed considerably from the other metal chelates in the acetylation reaction (26). Under the same conditions that had given extensive acetylation of the cobalt and chromium acetylacetonates, the rhodium chelate reacted very slowly and formed only a small amount of the monoacetylated compound (XX). Fortunately, the hydrolytic stability of rhodium acetylacetonate is such that the Friedel-Crafts reaction can be carried out under vigorous conditions that would rapidly degrade the chromium and cobalt chelates. Thus treatment of rhodium acetylacetonate with acetyl chloride and aluminum chloride in dichloroethane afforded the mono- and diacetylated chelates (XX and XXI). No triacetylated chelate was isolated from this reaction. In a similar manner butyryl-and benzoyl-substituted rhodium chelates (XXIII and XXIV) have been prepared. These and other experiments indicate that the rhodium acetylacetonate ring is less reactive than the cobalt or chromium rings. 

Treatment of allylpyridinium salts with weak bases gave ylides (152) an intramolecular 1,5-cyclization then yielded dihydroindolizines (153), which are prone to oxidation to (154). More than 90% of (153) is formed if R1 is phenyl and R2 is benzoyl or acetyl. If R is H or p-anisyl the indolizine (154) is the major product. 1,5-Cyclizations of ylides of the type (152) with a different substitution pattern have been investigated. This type of reaction seems to be somewhat unpredictable since the 1,5-cyclization is accompanied by 1,3-dipolar cycloadditions (Section 3.08.6.2.2) to a varying extent (75JCS(Pl)575). 

---