Organoboranes in organic synthesis: IX. Carbonylation products of organoboranes derived from myrcene

Myrcene and thexylborane react in the ratio $\text{2}\text{3}$ to give a mixture of two boranes, only one of which is carbonylated with cyanide/trifluoroacetic anhydride, followed by oxidation, to give 3-hydroxymethyl-6-isopropyl-2-methylcyclohexanone (A). The positions of hydroboration are established by synthesis of the hydroboration/oxidation products. The cyanidation of the organoboranes derived from myrcene and diborane leads to a $\text{2}\text{3}$ mixture of A and 5-(2′-hydroxyethyl)-2-isopropylcyclohexanone, the structures of which are established by independent synthesis. The hydroboration of myrcene is shown to be relatively non-stereospecific.     

Revision of an enamine synthesis; the preparation and reactions of 2-morpholinoisoflav-3-ene.

The condensation of $\text{N}$-styrylmorpholine with salicylaldehyde does $\text{not}$ give a product that can be oxidised to isoflavone; the product is $\text{N}$-morpholino-isoflav-3-ene which can be used to prepare other compounds related to isoflavan and upon oxidation gives 3-phenylcoumarin.     

Simple,inexpensive routes to E and Z zeatine ribosides and derivatives useful for immunoassay.

Allylic oxidation of 6-$\text{N}$-(3,3-dimethylallyl)adenosine $\text{1}$ gave $\text{trans}$ ($\text{E}$) zeatine riboside $\text{3}$, which was isomerized to the $\text{cis}$ ($\text{Z}$) isomer $\text{5}$ by u.v. irradiation. A method for the regiospecific 3′-$\text{O}$-succinoylation of these nucleosides is given.     

Asymmetric oxidation of achiral selenides to optically active selenoxides : Stereochemistry of the allyl selenoxide-selenenate [2,3] sigmatropic rearrangement

Asymmetric oxidation of methyl phenyl selenide ($\text{3}$), under anhydrous conditions, by chiral 2-sulfonyloxaziridines, $\text{1–2}$, gives optically active methyl phenyl selenoxide (8.1–9.3% ee). The stereochemistry of the selenoxide is determined by the configuration of the oxaziridine three membered ring with non-bonded steric interactions responsible for the chiral recognition. Asymmetric oxidation of E-phenyl cinnamyl selenide ($\text{7}$) by $\text{1–2}$ affords optically active l-phenylallyl alcohol ($\text{9}$). A concerted [2,3] sigmatropic rearrangement via an exo transition state is proposed.     

Structure of cypridina biluciferyl,a dimer of cypridina luciferyl radical having bioluminescent activity

Structure of $\text{Cypridina}$ biluciferyl (luciferyl radical dimer), which is produced by chemical oxidation of $\text{C}$. luciferin with such as ferricyanide, was determined to be the symmetric 5,5′-dimer of $\text{C}$. luciferin. It gives light in the presence of $\text{C}$. luciferase, although the bioluminescent rate is very low. We suggest that the biluciferyl is an intermediate in the oxidation of the luciferin to $\text{C}$. luciferinol.     

Pyridinium dichromate oxidation. Modifications enhancing its synthetic utility

An improved procedure is described for extremely rapid and efficient oxidation of alcohols, by adding a small quantity of $\text{anhydrous}$ acetic acid (AcOH) to pyridinium dichromate (PDC) and $\text{freshly activated}$ molecular sieve powder in CH₂Cl₂ at room temperature.     

Photoinduced cyclization of 3β-acetoxy-C(14a)-homo-B-norlanosta-8(14a),9(11)-diene as a route towards B(9a)-homo-C-norlanostane derivatives

The synthesis of diketones $\text{6}$, $\text{7}$ and $\text{8}$ starting from diene $\text{3}$ by photochemical cyclization followed by RuO₄ oxidation is described and stereochemistry of products is proposed.     

Isolation,Characterisation and Oxidation of Isomeric Ferrelactone Complexes.

Irradiation of 1,2-epoxy-l-vinylcyclopentane (1) in the presence of Fe(CO)₅ leads to the formation of isomeric $\text{syn}$-and $\text{anti}$- ferrelactones (2) and (3). The structures of these complexes were determined by X-ray crystallographic methods and on oxidation gave different ratios of β- and δ-lactones.     

Examples of transvesicular reactions

The oxidation of vesicle-entrapped Ellman's anion ($\text{1}$) by exovesicular $\text{o}$-iodosobenzoate ion ($\text{2}$) is a permeation-limited, transvesicular reaction; transvesicular esterolyses reactions are also illustrated.     

The dimesitylboron group in organic synthesis 8. Preparations of 1,3-diols from oxiranes

Alkyldimesitylboranes, yield anions¹, Mes₂B$\text{C}$HR, that on reaction with oxiranes followed by oxidation give 1,3-diols. These anions are thus the operational equivalent of R$\text{C}$HOH. The scope and limitations of the new process are delineated.     

Aminyl radical cyclization by means of anodic oxidation. Stereoselective synthesis of cis-1-methyl-2,5-disubstituted pyrrolidines

Neutral aminyl radicals generated by anodic oxidation of lithium alkenylamides 2 undergo a stereoselective cyclization to give $\text{cis}$-1-methyl-2,5-disubstituted pyrrolidines 4. Their $\text{cis}$ stereochemistry was confirmed by a comparison with $\text{trans}$-1,2-dimethyl-5-phenylpyrrolidine, the structure of which was established by X-ray crystallographic analysis of its quarternary ammonium bromide 6.     

Revised structure for fumarofine,an indenobenzazepine type alkaloid

Fumarofine is not a spirobenzylisoquinoline. Rather, it is the first know reduced indenobensazepine alkaloid, and possesses the cis B/C fused structure $\text{7}$. Rearrangement of synthetic spirobensylisoquinoline $\text{12}$ using methanesulfonyl chloride furnished indenobensazepine $\text{14}$. Osmium tetroxide oxidation of $\text{14}$ gave cis-glysol $\text{15}$. O-Methylfumarofine ($\text{8}$) was then obtained through pyridinium chlorochromate oxidation of $\text{15}$.     

Enantioselective synthesis of β-hydroxyisobutyric acid: a useful synthon in the synthesis of polypropionate-type natural products

The aldol reaction of formaldehyde with the dicyclopentylborinyl enolate derived from $\text{S}$-(or $\text{R}$-) 1-tert-butyldimethylsilyloxy-l-cyclohexylbutan-2-one, followed by desilylation and sodium meta-periodate oxidation, provides $\text{R}$-(or $\text{S}$-) β-hydroxyisobutyric acid.     

Silylated thiiran-1-oxides: Structure,ring opening and conversion to a benzothiophene.

Silylated thiirans upon oxidation with peroxyacids do not give exclusively the corresponding S-oxides but, in addition some products derived from ring opening. The stereochemistry of the oxidation to thiiran-1-oxides is $\text{anti}$ to the silyl group as demonstrated by X-ray analysis.     

Synthesis of novel neuroexcitatory amino acids derived from kainic acid

The synthesis of the novel epimeric amino acids $\text{5a}$ and $\text{7a}$ by oxidation of methyl ketones derived from kainic acid is described. On biological testing both compounds exhibit a strong neuroexcitatory activity.     

Novel intramolecular diels-alder reactions with alkynylthio derivatives of 1,2,4-triazines. New routes to thieno[2,3-b]pyridines and thieno[2,3-c]pyridines.

S-Alkylation of 1,2,4-triazine-6-thiones with 4-iodobutyne, followed by oxidation to the sulfoxide and intramolecular cycloaddition (at room temperature),gives 2,3-dihydrothieno[2,3-$\text{c}$]pyridines, which are readily dehydrated with acetic anhydride to thieno[2,3-$\text{c}$]pyridines. The same series of reactions carried out on 1,2,4-triazine-3-thiones leads to thieno[2,3-$\text{b}$]pyridines.     

Syntheses of “thiiranoradialenes”

A stable tetramethylthiiranoradialene, 2,3-diisopropylidenethiirane $\text{6}$, was prepared by pyrolysis of lithium salt of tosyl hydrazone of 2,2-dimethyl-4-isopropylidene-3-thietanone. The corrsponding sulfoxide $\text{7}$ was also prepared by oxidation of $\text{6}$.     

A biosynthetic approach to the structure of eumelanins. The isolation of oligomers from 5,6-dihydroxy-1-methylindole.

Enzymic oxidation, or autooxidation at pH 9, or$\text{1}$ led to a mixture of fluorescent products the major of which could be isolated, as the acetyl derivative, and identified as 5,6,5',6'-tetraacetoxy-1,1'-dimethyl-2,4'-biindolyl ($\text{6}$). In the presence of metal cations, e.g. Ni²⁺, autooxidation of $\text{1}$, at pH 7.5, led to the isolation, besides the dimer $\text{6}$ in lower amounts, of two more oligomers which were formulated as 5,6,5',6'-tetracetoxy-1,1'-dimethyl-2,2'-biindolyl ($\text{7}$) and 5,6-diacetoxy-1-methyl-2,4-di-[5',6'-diacetoxy-1'-methy1-2'-indolyl]-indole ($\text{8}$). The unexpected reactivity of $\text{1}$ to undergo oxidative coupling at 2- and 4- position rather than at 3- and 7- position, as previously believed, is discussed in relation to the current views on the structure and biosynthesis of eumelanins.     

Synthesis of ansamycins: An approach to the naphthoquinone portion of the rifamycins and streptovaricins

Naphthoquinone $\text{1}$, a fully functionalized model for intermediates in ansamycin synthesis, was prepared by the intramolecular Claisen condensation of benzofuran $\text{9}$ followed by oxidation of the novel tricyclic compound $\text{10}$.     

Efficient total syntheses of polygodial and drimenin.

A short and stereoselective total synthesis of (±) polygodial and drimenin is presented. The efficiency of the synthesis is due to the easy access to intermediate diol $\text{4}$ and its successful direct oxidation into polygodial.