Noncyclic Derivatives

HB(N=CH2)2. Geometry-optimization calculations were performed at the 6-31G level on one staggered and three planar conformations of HB(NCH2)2 see Fig. 4-37 [2]. Calculated data are compiled in Table 4/10. 

The Optimized Geometry and Electron Distribution of HB(NCH2)2 as Obtained by 6-31G Calculations [2]. 

Likewise, the (E)-conformers of ROCH=CHCH2B[N(CH3)2]2 with R = CH3 or (CH3)3SiCH2CH2 were prepared from the corresponding (E)-1-alkoxy-3-phenylthiopropenes, potassium naph-thalenide, and CIB[N(CH3)2]2. The H NMR and NMR spectra are given [34]. 

CgH5B[N(CH3)2]2 reacts with 2-(plperldln-2-yl)ethanol In refluxing benzene to yield 2-phenyl-1,3,2-oxazaborabicyclo[4.4.0]decane [8]. C6H5B[N(CH3)2]2 is used in the characterization of diols as phenylboronate esters [9]. 

Additional diaminoboranes of the types RB(NR R2)(NR3R ) and RB(NR R )N3 are compiled in Table 4/11, and those of the type RB(NR R )(NR BXY) are presented in Table 4/12, p. 171. Diaminoboranes containing the N-(B-0)-N sequence will be covered in Boron Compounds 4th Suppl. Vol. 3b, to be published, Section 4.3. 

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In the case of noncyclized derivatives of the aromatic series (nitrotolanes), isato-gen is obtained either by a longer heating of the substrate in pyridine, or by photochemical (sun rays) or catalytic action (69MI2) (Scheme 113). 

Complexation studies were carried out by electrospray ionization mass spectrometry (ESI-MS) with three lanthanides (La, Eu, and Yr) at a concentration of 10 4 M, while the ratio of concentration of CPw2 versus calixarene (r = [calix]org/[Ln]aq) was varied between 0.1 and 10.165 The behavior of the three lanthanides is the same the 1 1 Ln calix-CMPO complex is always predominant in the range of concentration studied the 2 1 Ln calix-CMPO appears in the case of metal excess with a maximum for r = 0.5, while the percent of 1 2 Ln calix-CMPO increases as the concentration of ligand increases, but does not exceed 10% for r = 10. These studies show that two factors play a key role in the selectivity of CMPO derivatives, firstly the presence of phenyl groups on the phosphorus atom, which confers the selectivity to CMPO ligands, secondly the calixarene structure, which amplifies this selectivity due to its preorganization. Indeed the noncyclic derivative (Os2), in spite of the presence of phenyl units, does not display noticeable selectivity. 

From a molecular biology point of view it is interesting to note the same enantiopreference than in the ofloxacin and flumequine series. In addition the potency of 2 -trans-phenylcyclopropyl derivatives provide further example indicating substantial bulk tolerance at N-1. The reason for obtaining an optimum of activity for N-ethyl in aliphatic and noncyclic derivatives must lie elsewhere. 

The result is explained by considering the stacking structure between the quinoline moiety and the benzene ring linked to the carboxylic acid, which gives the cavity size adequate for Li+. (Fig. 3) Several selective host molecules for Li+ such as [13]crown-4 18), [14]crown-4 19), [16]crown-4 20>, or noncyclic polyether amide derivatives 21) also possess trimethylene moiety, and this is an interesting finding from the point of view of molecular design of new host molecules for Li+. 

Okahara, M., and Nakatsuji, Y. Active Transport of Ions Using Synthetic Ionophores Derived from Cyclic and Noncyclic Polyoxyethylene Compounds. 128, 37-59 (1985). 

It must be noted that the cyclic model fails to account for the role of the additional alkyllithium and diethylaluminum that are required in precise amounts to achieve high selectivity. A simple model that recognizes a possible role for the additional reagents suggests the intermediacy of an extended, noncyclic transition state G with the aldchydic oxygen coordinated to some undefined Lewis acidic species derived from the additional components of the reaction mixture26,44. Aggregates composed of enolate, alkyllithium and dialkylaluminum species are also possible. 

Many other cyclic and noncyclic organic carriers with remarkable ion selectivities have been used successfiilly as active hosts of various liquid membrane electrodes. These include the 14-crown-4-ether for lithium (30) 16-crown-5 derivatives for sodium bis-benzo-18-crown-6 ether for cesium the ionophore ETH 1001 [(R,R)-AA -bisd l-ethoxycarbonyl)undecyl-A,yVl-4,5-tctramcthyl-3,6-dioxaoctancdiamide] for calcium the natural macrocyclics nonactin and monensin for ammonia and sodium (31), respectively the ionophore ETH 1117 for magnesium calixarene derivatives for sodium (32) and macrocyclic thioethers for mercury and silver (33). 

Camphor-derived sulfonamide can also permit control of enantioselectivity by use of additional Lewis acid. These chiral auxiliaries can be used under conditions in which either cyclic or noncyclic TSs are involved. This frequently allows control of the syn or anti stereoselectivity.143 The boron enolates give syn products, but inclusion of SnCl4 or TiCl4 gave excellent selectivity for anti products and high enantioselectivity for a range of aldehydes.145... 

Photochemical behaviour of compounds 83-86 [33] in the gas phase has been reported, in order to distinguish between silyl radical and silylene formation. Photolysis of the noncyclic precursors 83 and 84 gave products derived from silyl radicals, which come from a direct Si—Si bond homolysis, with a little evidence of silylene formation. In contrast, dimethylsilylene (Mc2Si ) was observed as a direct photoproduct from the cyclic precursors 85 and 86. The reaction sequence including a Sni step shown in Scheme 6.18 for the formation of dimethylsilylene was proposed to explain the different observations for cyclic and noncyclic systems. 

Saa and coworkers reported a remarkable cycloisomerization of alkynal to cycloalk-ene derivatives with loss of a CO molecule [30] some examples are shown in Table 6.3. Heating 5-alkynal 94a in AcOH (90 °C, 24h) with [Ru(Cp)(CH3CN)3]PF6 (5 mol%) afforded the cyclopentene derivative 9Sa in 90% yield. Ketone 94e afforded the cyclopentene 9Se in moderate yield, whereas the ester 94f gave the noncyclized product 96 with loss of one carbon unit (Table 6.3) (Scheme 6.32). 

Skattebol [12], on the other hand, could not detect such carbene intermediates by their addition product (spiropentanes) to olefins using gem-dibromo-cyclopropanes derived from noncyclic olefins. 

Tetrahydrothiopyran and its simply substituted derivatives are to be regarded as cyclic sulfides, and in consequence their chemistry is analogous to that of their acyclic counterparts, which is extensively covered in the standard texts (B-79MI22500). Oxidation, alkylation, halogenation, etc. reactions differ from the corresponding phenomena in the noncyclic species only in so far as the stereochemical constraints imposed by a more rigid framework control the orientation of reactants, transition states and products. 

Whereas Kucherov and co-workers99 had previously obtained only noncyclized products of type 64 and 65 from the reaction of 2-amino-5-halopyridines and diethyl malonate, Lappin et al.91 succeeded in cyclizing the 5-halo (Cl and Br) derivatives of 64 to pyrido[l,2-a]pyrimidines (63) by applying semimicro sublimation to induce cyclization. 

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