Trimeric Lewis* synthesis

Nilsson, M, Norberg, T, Synthesis of carbohydrate derivatives corresponding to a tumor-associated glycolipid a trimeric Lewis nonasaccharide and a trimeric A-acetyl lactosamine hexasaccharide, J. Carbohydr. Chem., 8, 613-627, 1989. 

Koeller, K M, Wong, C H, Chemoenzymafic synthesis of sialyl-trimeric-Lewis, Chem. Eur. J., 6,... 

In a few cases, the synthesis was directed towards well-defined oligomers (dimers, trimers, etc.). The synthesis of bis(5,7,3, 4 -tetra-0-benzyl)-EC 4/1,8-dimer from 5,7,3, 4 -tetra-0-benzyl-EC and 5,7,3, 4 -tetra-0-benzyl-4-(2-hydroxyethoxy)-EC was described by Kozikowski et al. [41]. This compound exhibited the ability to inhibit the growth of several breast cancer cell fines through the induction of cell cycle arrest in the Gq/Gi phase. Analogously, procyanidin-B3, a condensed catechin dimer, has been obtained through condensation of benzylated catechin with various 4-0-alkylated flavan-3,4-diol derivatives in the presence of a Lewis acid. This reaction led to protected procyanidin-B3 and its diastereomer. In particular, octa-O-benzylated procyanidin-B3 has been produced with high levels of stereoselectivity and in excellent isolation yields [42]. 

Bis(dichloroboryl)benzene (6) is an important starting material which lends itself to facile derivatization. As shown by Piers, it cleanly reacts with bis(penta-fluorophenyl)zinc to afford the corresponding bidentate Lewis acid 13 (Scheme 7) The molecular structure of diborane 13 has been determined and is shown in Fig. 1. In this structure, the vicinal boron atoms are held at 3.26 A and from one another and seem to be ideally positioned to cooperatively interact with monoatomic anions. The fully fluorinated version of this bidentate Lewis acid has also been prepared. Original efforts focused on the use of 1,2-bis(dichloroboryl)tetrafluorobenzene 14 as a starting material (Scheme 8). This compound could be observed in the early stage of the reaction of trimeric perfluoro-o-phenylenemercury (4) with boron trichloride, but was found to be unstable toward condensation into 9,10-dichloro-9,10-dihydro-9,10-diboraoctafluoroanthracene 15. The successful synthesis of the fully fluorinated... 

In another research laboratory, surprised by the lack of success of other research groups and the previous statements about the impossibility of applying biocatalytic chemistry to polithiophenes and polypyrroles, special attention was paid to the enzymatic polymerization of the EDOT monomer [43]. In this case, the first trials succeeded and a blue-colored polymer solution was obtained after 16h of reaction (Scheme 4). As is well-known, an acidic reaction medium is suitable to increase the rate of polymerization. Protonic acids and a variety of Lewis acids catalyze the equilibrium reaction of EDOT to the corresponding dimeric and trimeric compounds without further oxidation or reaction [44]. In this work, three different pHs were evaluated (pH = 2, 4, and 6) in order to establish the optimum for adequate synthesis of EDOT. The UV-visible (UV-Vis) spectra for these three reactions are... 

Since Hausmanrfs and Kipping s initial studies, the synthesis of truxene from 1-indanone has been carried out many times under a wide variety of conditions. Reagents that have been reported to promote this trimerization are generally either strong protic acids or Lewis acids and include hydrochloric acid [15], hydroiodic acid [15], phosphorus pentoxide [15], zinc dust [15], sulfuric acid [17], phosphorus pentachloride [17], zinc chloride in acetic acid [18],... 

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