Synthesis of novel cage oxaheterocycles

m-CPBA-promoted Baeyer-Villiger oxidation of pentacyclo[6.3.0.0(2,6).0(3,10).0(5,9)]undecan-4-one (1) afforded the corresponding lactone 2 in 93% yield. Lithium aluminum hydride promoted reduction of lactones 2, 6, and 9, performed in the presence of BF(3).OEt(2) reagent, afforded the corresponding cage ethers, i.e., 4, 7, and 10, respectively. Two methods that can be used to replace a cage C=O group by ether oxygen without concomitant rearrangement are delineated. A key step in the first of these methods employs m-CPBA promoted "double Criegee rearrangement", which was used to convert pentacyclo[6.3.0.0(2,6).0(3,10).0(5,9)]undecan-4-one diethyl acetal (11) into 7,9-dioxapentacyclo-[8.3.0.0(2,6).0(3,12).0(5,11)]tridecan-8-one (12). Subsequently, 12 was converted into 4-oxapentacyclo[6.3.0.0(2,6).0(3,10).0(5,9)]undecane (14) via a two-step reduction-dehydration reaction sequence. The second method utilized PhI(OAc)(2)-I(2) reagent to convert cage lactols 15 and 17 into the corresponding cage ethers, i.e., 14 and 2-oxaadamantane (18), respectively.     

Slow equilibration of reversed-phase columns for the separation of ionized solutes

Reversed-phase columns that have been stored in buffer-free solvents can exhibit pronounced retention-time drift when buffered, low-pH mobile phases are used with ionized solutes. Whereas non-ionized compounds exhibit constant retention times within 20 min of the beginning of mobile phase flow, the retention of ionized compounds can continue to change (by 20% or more) for several hours. If mobile phase pH is changed from low to high and back again, an even longer time may be required before the column reaches equilibration at low pH. The speed of column equilibration for ionized solutes can vary significantly among different reversed-phase columns and is not affected by flow rate.     

NMR Characterization of the Na(3)AlP(3)O(9)N and Na(2)Mg(2)P(3)O(9)N Nitridophosphates: Location of the (NaAl)/Mg(2) Substitution

We report a solid state nuclear magnetic resonance study of (23)Na, (27)Al, and (31)P in two crystalline nitridophosphate phases, Na(3)AlP(3)O(9)N and Na(2)Mg(2)P(3)O(9)N, including two-dimensional multiple-quantum magic angle spinning (MQ-MAS) experiments on (23)Na to separate overlapping lines. The previously described single-crystal structure of Na(3)AlP(3)O(9)N gives crystallographic examples of Al(OP)(6) and P(O[Al,Na])(2)(ONa)(N[P,Na]) environments and three different environments of sodium: two Na(O)(6) and one Na(O)(6)(N). From these observations we characterize the modification of the local environment of phosphorus and show that Mg only substitutes Na in the Na2 site of the Na(2)Mg(2)P(3)O(9)N structure.     

Addition of trimethylsilyl azide and of “mixed anhydrides” to the N-C(3) σ-bond in 3-substituted-1-azabicyclo[1.1.0]butanes

Trimethylsilyl azide adds smoothly to the highly strained N-C(3) σ-bond in 3-ethyl-1-azabicyclo[1.1.0]-butane ( 1 ) to afford an adduct, 2 , that reacts in situ with a variety of electrophilic reagents (i.e., ethyl chloroformate, p-toluenesulfonyl chloride, benzoyl chloride, acetyl chloride, and oxalyl chloride) to afford the corresponding N-substituted-3-azido-3-ethylazetidines 3–7 , respectively in 62–72% yield. Similarly, 1 reacts regiospecifically with “mixed anhydrides” (i.e., p-toluenesulfonyl acetate, methanesulfonyl acetate, and benzoyl trifluoromethanesulfonate) to afford the corresponding adducts, 8–10 , respectively) in 38–68% yield. Reaction of p-toluenesulfonyl azide with 1-aza-3-phenylbicyclo[1.1.0]butane ( 12 ) produces two products: N-(p-toluenesulfonyl-3-azido-3-phenylazetidine ( 13 , 15%) and a dimeric product, N-(N'-p-toluenesulfonyl-3′-phenyl-3′-azetidinyl)-3-azido-3-phenylazetidine ( 14 , 28%). Ethyl chloroformate adds to the N-C(3) σ-bond in 1-aza-3-(bromomethyl)bicyclo[1.1.0]butane ( 15 ) to afford N-carboethoxy-3-(bromomethyl)-3-chloroazetidine ( 16 ) in 73% yield.     

Molecular design of lipophilic disalicylic acid compounds with varying spacers for selective lead(II) extraction

Lipophilic disalicylic acids 5,5'-decyl-2,2'-[1,2-ethanediylbis(oxy)]bisbenzoic acid (1), 5,5'-decyl-2,2'-[1,3-propanediylbis(oxy)]bisbenzoic acid (2), 5,5'-decyl-2,2'-[oxybis(1,2-ethanediyl-oxy)]bisbenzoic acid (3), 3,5-bis[2'-(2'-carboxyphenoxy)ethyl]-4-oxahexacyclo-[5.4.1.0(2,6).0(3,10).0(5,9).0(8,11)]dodecane (4), and 1,3-bis[2'-(2'-carboxyphenoxy)ethyl]adamantane (5) are evaluated as selective Pb(II) extractants. The solvent extraction of Pb(II) and of Cu(II) from buffered aqueous solutions of varying pH into chloroform by ligands 1-5 is examined in relation to the molecular structure of the dicarboxylic acid extractant. Ligand 1, with an ethylene spacer between two lipophilic salicylic acid units, exhibits excellent extraction selectivity for Pb(II) over Cu(II). Lengthening the spacer in ligands 2 and 3 diminishes both the extraction efficiency and selectivity. Ligands 4 and 5, with rigid spacer units, show significant reductions in both Pb(II) and Cu(II) extraction. Slope analysis reveals that ligand 1 reacts in a 2:1 stoichiometry with Pb(II) in extraction, which differs from the 1:1 stoichiometries for 2 and 3. The differences in the half extraction pH (DeltapH(1/2)) values for Pb(II) and Cu(II) extraction are 1.29, 0.49, and 0.48 for 1-3, respectively.