Development of a synthetic route led to the synthesis of the tetracyclic compound 76a, a key intermediate for continued studies on the total synthesis of naphthyridinomycin.

Identity rate constants were measured for the reaction of arylphenylsulfides with arylphenylsulfonium triflates in sulfolane, with the aim of using these as input for the Marcus equation and to find the transition state charge distribution. The rate constant for the reactions of N-methylbenzonitrilium triflate with 4-methylbenzonitrile was estimated. The rate and equilibrium constants were determined for the reaction of several arylmethylselenides with both phenylselenide ion and 4-methoxyphenylselenide ion resulting Hammett $\rho$ values of +1.80 and +2.02 respectively. The equilibrium constants for these species produced a Hammett $\rho$ value of +4.20. Using the Marcus equation, calculated plots of log k versus log $K\sb{\rm eq}$ for several different work terms and a constant intrinsic barrier showed only a small amount of curvature over a range of 10$\sp{12}$ in equilibrium constant. Thus, a series of reactions over a small range of equilibria will not show any appreciable curvature. Rate constants for the reaction of iodide ion with methyl triflate and with dimethylsulfate were measured by stopped-flow techniques. The experimental rate constants differed by only a small amount from those calculated by the Marcus equation.

Sesbanine (5) is a novel cytotoxic alkaloid that was isolated from seed extracts of Sesbania drumondii $\sp{1,2}$ (Leguminosae). The biosynthesis of sesbanine was approached by dividing the molecule into two moieties, the pyridine ring moiety (A) and the cyclopentanol ring moiety (C). Evidence is offered which indicates that the pyridine ring moiety (A) arises from one unit of nicotinic acid. It was demonstrated that nicotinic acid is derived from tryptophan in Sesbania and that tryptophan also serves as a specific precursor of sesbanine via nicotinic acid. The cyclopentanol moiety (C) was shown to be derived from shikimic acid via p-hydroxybenzoic acid. Investigations of the biosynthesis of the unusual phytotoxic coronatine (20) have shown that the toxin is formed in a novel manner. It has been demonstrated that the hydrindanone moiety (21) of the toxin is assembled from the head to tail linkage of five acetate units with C-2 and C-3 of pyruvate serving as a starter unit. The mechanism for formation of the C-C single bonds between C-3 of pyruvate and C-2 of two acetate units is presently obscure. The 1-amido-1-carboxy-2-ethylcyclopropyl moiety (22) of the toxin is derived by an unprecedented cyclization of the amino acid isoleucine.

Part I. The tritium isotope effect for hydrogen atom abstraction by the 1-adamantyl radical in cyclohexane was determined to be 103, confirming the exceptionally large deuterium isotope effect found earlier for this process. While the Noyes model accounts for the cage effect in the thermolysis of cis -1-azoadamantane, the non-linear correlation between the yield of cage dimer and solvent fluidity at high viscosities suggests that microviscosity influences the breakdown of the solvent cage. In acetonitrile, 1-adamantyl radicals were found to abstract hydrogen atoms or to add to the nitrile function. The products of cross-recombination between the resulting radicals were identified and quantified. Part II. The carbon-centered $\beta$-azo radical was calculated to fragment under formation of nitrogen with an exothermicity of $\sim$10 kcal/mole. The generation of such a $\beta$-azo radical was attempted by homolytic fragmentation of five acyclic and cyclic $\beta$-substituted azo compounds. Although concerted decomposition of these compounds could cause a drastic rate enhancement, our azo compounds exhibited only a slight rate enhancement (1.5-9 fold) in comparison to the unsubstituted azo compounds. The radical stability of the $\beta$-substituent exerted no influence on the rate of azo fragmentation. The high temperature required for pyrolyses (180$\sp\circ$C) led to complicated product mixtures due to competing bond scission between the azo moiety and the $\beta$-substituent, as well as the decomposition of primary thermolysis products. For $\beta$-azo phosphinites and $\beta$-azo carbonates, the fragmentation was governed by both ionic and radical processes. The tin hydride reduction of a cyclic $\beta$-azo xanthate at room temperature proceeded via intramolecular radical attack on the azo linkage to yield an unusual cyclic thiourea rather than by loss of N$\sb 2$.

Part I. Novel mercaptoethoxy and mercaptoxylyleneoxy derivatives of meso-tetraphenylporphyrin, H$\sb2$TPP, and meso-tetranaphthalporphyrin, H$\sb2$TNP, with the potential for coordinating an iron-sulfur cubane cluster, have been synthesized and characterized. The thiol function is guarded during synthesis by an acetate protecting group, which is removed quantitatively by an acid-catalyzed hydrolysis reaction in the final workup step. The four "thiol-arms" on these light-sensitive porphyrins allows for the presence of atropisomers which have been observed and, in the case of the tetranaphthalporphyrin derivative, separated. The atropisomers of the acetylmercaptoxylyleneoxy derivatized tetraphenylporphyrin, H$\sb2$TAMXPP, interconvert at a rapid rate and are only observable by $\sp1$H NMR spectroscopy at $-$70$\sp\circ$C. The free-base porphyrins, in the thiol-protected form, are easily metallated by literature procedures and the zinc(II) and iron(III) chloro derivatives of these new porphyrin compounds have been synthesized and characterized. Part II. The thiol functionality of the mercaptoxylyleneoxy derivative of tetraphenylporphyrin, H$\sb2$TAMXPP, readily exchanges for ethanethiol when H$\sb2$TAMXPP is reacted with (Fe$\sb4$S$\sb4$(SEt)$\sb4\rbrack\sp{2-}.$ The dioxygen and light sensitive product, (cation)$\sb2$ (Fe$\sb4$S$\sb4$(H$\sb2$TMXPP)) has been isolated and characterized. Mossbauer and $\sp1$H NMR spectroscopy provide evidence for the successful synthesis of the desired porphyrin/iron-sulfur cluster compound. As such, this compound is the first example for the synthesis and isolation of a 1:1 porphyrin/iron-sulfur cluster compound and provides as a first generation model compound for the siroheme/iron-sulfur cluster structural unit found at the active site of sulfite reductase.

Various methods of synthesizing the novel, highly congested bis(tris(trimethylsilyl)methyl) disulfide (2) were investigated. / It was found that the oxidation of tris(trimethylsilyl)methyl mercaptan (1) with iodine in the presence of sodium methoxide affords a product whose $ sp{13}$C, $ sp1$H and combustion data are consistent with its structure being that of 2. In another attempt at the preparation of 2, tris(trimethylsilyl) methane with methyl lithium, elemental sulfur and iodine gave rise to 2 unanticipated products, believed to be bis(trimethylsilyl)methyl, tris(trimethylsilyl)methyl disulfide (3a) and bis(tris(trimethylsilyl)methyl) trisulfide (3c). / Furthermore, trisulfide 3c was subsequently prepared by the sulfuration of 1 using SCl$ sb2$ or N,N-thiobisbenzimidazole. In addition to thiol 1, both 3c and 2 exhibited unanticipated multiplicity of $ sp{13}$C NMR peaks in the silyl region of the spectrum. As a result, efforts were made to explain these results by molecular mechanics calculations on the thiol, trisulfide and disulfide structures.

The chelating effect on regio- and stereochemical control of the homoallyl alcohol synthesis and electrophilic substitution of allylsilane was studied, using 2,2-dimethyl-1-$ {$1- ((S)-2-(2-methoxyethoxy)methyl) pyrrolidinyl$ }$-2-sila-4-pentene (S1) and 2,2-Dimethyl-1-$ {$1- ((S)-2-hydroxymethyl) pyrrolidinyl$ !$-2-sila-4-pentene (S2), with S1 synthesized from L-Prolinol. / The synthesis of homoallyl alcohol was carried out by allyl transformation from S1 and S2 to a Lewis acid activated aldehyde. Chelation between the allylsilyl ligand and the Lewis acid:aldehyde complex was found to favor the cyclic syn-clinal over the acyclic anti-periplanar transition state, in the asymmetric synthesis of the alcohol 1-dodecen-4-ol (P1). The bulky, remote and weak chelating ligand resulted in only modest selectivity and average chemical yield. / Regio- and stereochemical control of the electrophilic alkylation of allylsilanes S1 were achieved due to chelating effect that favored $ alpha$-alkylation. The chiral chelating ligand also resulted in enhanced stereochemical control electrophilic alkylation. Steric effect, due to a large electrophile, and solvent effect that causes disruption of the chelated complex, decrease $ alpha$-selectivity.

No description available.

Fluoride ions smoothly destannylate organotin oxides, sulfides and selenides to liberate highly nucleophilic species ("S$ sp{2-}$", RS$ sp-$, RO$ sp-$, RSe$ sp-$, etc.). Also, the first nucleophilic oxide "O$ sp{2-}$" and selenide "Se$ sp{2-}$" transfer agents are reported. The tin atom thus serves as a general "group 16 (VIB) transfer agent". In the presence of crown ethers or ammonium salts, this process results in a new way to generate "naked" nucleophiles. Novel anhydrous fluorinating systems (CsF and crown ethers) involving solid-liquid phase transfer catalysis have been designed and studied. In addition, C-C bond forming reactions have been investigated by fluorodestannylation. As an extension of these results, fluorodegermanylation and fluorodeplumbylation reactions are reported. As a generalization, fluoride ion demetalates the whole group 14 for releasing nucleophilic species. Some pentacoordinated intermediates have been observed by $ sp{19}$F and $ sp{119}$Sn NMR spectroscopy in fluorodestannylation, thus confirming the model of nucleophilic substitution at tin and silicon. Mechanistic aspects are discussed along with a possible metal proximity effect in the enhancement of the nucleophilicity of an anion. Finally, in the presence of silver salts, bis(tributyltin) oxide acts as a mild oxygen transfer agent in converting primary organic iodides and bromides to alcohols.

The efficiencies of many rigidly held cis-aquahydroxotetraazacobalt(III) complexes in promoting the hydrolysis of phosphate esters (BDNPP, BNPP, NPP) have been compared. The phosphate diester bond in ((trpn)Co(OH)(BNPP)) $ sp{+}$ is hydrolyzed at about the same rate as BNPP bound to a real enzyme from Enterobacter aerogenes and about 10$ sp{10}$ times more rapidly than free BNPP. The dramatic increase in the activity of the Co(III) complex with change in the tetraamine ligand structure can be explained in terms of a detailed mechanism of the reaction. / Co(III) complexes, ((tren)Co(OH$ sb2)$(OH)) $ sp{2+}$ and ((trpn)Co(OH$ sb2)$(OH)) $ sp{2+}$ have been shown to be highly efficient in promoting the hydrolysis of phosphate di- and monoesters with poor leaving groups. ((trpn)Co(OH$ sb2)$(OH)) $ sp{2+}$ promoted hydrolysis of phosphate monoesters leads to a novel binuclear phosphato complex which is a model for the active site of Purple Acid Phosphatases. / For the first time it has been shown that hydrolysis of carboxylic esters catalyzed by ((trpn)Co(OH$ sb2)$(OH)) $ sp{2+}$ is truly catalytic. The hydrolytic activity of ((trpn)Co(OH$ sb2)$(OH)) $ sp{2+}$ has been linked to the fact that this complex chelates carboxylic acids as shown by $ sp{13}$C NMR spectroscopy and the crystal structure of ((trpn)Co($ eta sp2$-OCC(CH$ sb3) sb3) rbrack sp{2+}$. This complex is the first example of a cobalt(III) complex in which carboxylic acid is chelated.