DABCO l,4-diazabicyclo

DABCO = l,4-diazabicyclo[2,2,2]octane (triethylene diamine) (22) is a moderately basic amine, removable by sublimation, that causes enantiomeriza-tion of amino acid residues that have been reacted to form Schiff s bases (RR C=NCHR2CO-). 

The propertiesof DABCO (l,4-diazabicyclo[2.2.2]octane) are of considerable interest. The in- and out-of-phase interaction of the two occupied sp3 hybridized lone pairs on the two nitrogen atoms may be described by an interaction diagram such as shown in Figure 3.5b. 

Subjection of this material to a formylation protocol involving a Rh catalyst, a bulky phosphite and DABCO (l,4-diazabicyclo[2.2.2]octane) in the presence of H2/CO gas mixture, gives a high yield of the desired aldehyde. Iteration of these steps leads to the synthesis of Tolypothrix pentaether. 

Abbreviations Ac, acetyl AIBN, 2,2 -azobisisobutyronitrile All, allyl Alloc, allyloxycarbonyl Bn, benzyl BOM, benzyloxymethyl BPC, p-phenylbenzoyl Bu, butyl t-Bu, tert-butyl Bz, benzoyl CAN, ammonium hexanitratocerate (IV) Cbz, bezyloxycarbonyl CDl, carbonyldiimizazole ClAc, chloroacetyl Cp, cyclopentadienyl CSA, DL-lO-camphorsulfonic acid DABCO, l,4-diazabicyclo[2.2.2]octane DAST, diethylaminosulfur trifluoride dba, dibenzylideneacetone DBU, l,8-diazabicyclo[5.4.0]undec-7-ene DCC, iV,iV-dicyclohexylcarbodiimide DDQ, 2,3-dichloro-5,6-dicyano-l,4-benzoqui-none DEAD, diethyl azodicarboxylate DEIPS, diethylisopropylsilyl DIBAL, diisobutylaluminum hydride DMAP,... 

Figure 22. Photoionization map for DABCO (l,4-diazabicyclo[2,2,2]octane). The sloping feature at the upper left is a product of this form of representation it really represents electrons of fixed energy of 17.3 eV, from photoionization to an inner valence band of the singly charged ion, which autoionizes to the dication ground state. The extreme hollowness of the distribution for forming the dication in its lowest state (charges on the two N atoms) is also apparent.

Fig. 36. General acid-catalysed aminolysis of isocyanic acid [121] Eigen type curvature consistent with diffusion limiting proton transfer. CA, chloroacetic acid Dabco, l,4-diazabicyclo-(2,2,2)-octane AC, acetic add AN, anilinium ion PM, iV-propargylmorpholinium ion CEM, 2-chloroethylmorpholinium ion, MeM, iV-methylmorpholinium ion EG, ethyl glycinate BOR, boric acid MBA, methyl j8-alaninate ET, ethylammonium ion Q, quinuclidinium ion PIP, piperidinium ion ACET, acetamidinium ion Gu, guanidium ion.

There are only a few reports on successful metallations of simple saturated sulfides [1-3]. Lithiation of dimethyl sulfide has been achieved with BuLi.TMEDA in hexane [1], while methyl phenyl sulfide can be specifically converted into LiCH2SPh using BuLi.TMEDA or BuLi.DABCO (l,4-diazabicyclo[2,2,2]octane). These reagents do not give good results in attempts to lithiate the homologues, RCH2SPh. 

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