F. Walls

Alkaloids from stemmadenia species-I: The alkaloids of S. Donnell-Smithii and S. Galeottiana

Abstract —From Stemmadenia Donnell-Smithii and S. Galeottiana , the following new alkaloids were isolated: (+)-quebrachamine (IV), an optical isomer of the known (−)-quebrachamine; iso voacangine (IIIa), a position isomer of voacangine (Ia), voacamine, tabernanthine (IIIb) and ibogamine.

Selective reduction of aromatic nitro compounds containing o- and n-benzyl groups with hydrazine and raney nickel

Abstract The selectiity in the catalytic reduction of aromatic nitro compounds containing O-benzyl, N-benzyl or chlorine with hydrazine and Raney nickel was studied.

Studies in perezone derivatives : Structures of the pipitzols and perezinone

Abstract α and β-pipitzols isolated from the roots of Perezia cuernavacana and obtained by thermal rearrangement of perezone, (II), have been shown to be sesquiterpenes with structures IIIa and IVa related to cedrene (XXIII). The structure of perezinone has been revised and established as shown in formula XXVI.

Synthesis of enantiomerically pure 2-amino alcohols from amino acids mediated by sulfoxides

Abstract Enantiomerically pure (R1,S2)- and (S1,S2)-2-amino alcohols can be easily synthesized by stereodivergent reduction of α′-(N-Boc)amino β-keto sulfoxides (easily synthesized from readily available N-Boc amino ester hydrochlorides) with DIBAH (de 82–92%) and DIBAH/ZnBr2 (de 80%), followed by hydrogenolysis of the C–S bond of the resulting hydroxy sulfoxides and final hydrolysis of the N-Boc protecting group.

Asymmetric synthesis of α-acetylenic epoxides

Abstract Chiral α-acetylenic oxiranes were easily synthesized from readily available propargylic esters by a four-step sequence involving the stereoselective reduction of α′-alkynyl β-keto sulfoxides with DIBAH (de 66–78%) and DIBAH/ZnBr2 (de 78–88%), followed by further reduction of the resulting hydroxy sulfoxides into the corresponding sulfenyl derivatives and final epoxy ring closure via sulfonium salt.

Isomerization of Perezone into Isoperezone and Preparation of Dihydroisoperezinone

Abstract The reaction of perezone 1 with 3,4,5,6-tetrahydro-2-pyrimidinethiol 11 promotes a 1,2-carbonyl transposition in the quinoid ring of 1 giving rise to isoperezone 8, which treated with BF3·Et2O produces dihydroisoperezinone 9.

A stereodivergent approach to syn- and anti-β-hydroxy-γ-amino acids. Enantioselective synthesis of N-Boc-statine and N-Boc-3-epistatine mediated by sulfoxides

Abstract Asymmetric syntheses of the syn- and anti-stereoisomers of N-Boc statine, based on the stereodivergent reduction of a single sulfoxide 5, derived from N-Boc- l -leucine, are reported.

FURTHER STUDIES ON HYDROXYPEREZONE DERIVATIVES

Abstract Hydroxyperezone monoangelate ( 2c ) was transformed into the mixture of α-( 8 ) and β-perezols ( 9 ). Separation of these compounds permitted stereochemical assignments by NMR and ORD. The position of the angeloyl moiety in 2c was independently tested by its conversion to O-methylhydroxyperezone ( 1d ) identified with a sample synthesised from perezone ( 1a ). Several reactions distinguished the natural hydroxyperezone ( 2a ) from the synthetic hydroxyperezone hydrate ( 3 ).

A Simple Method to Prepare Alkyl 3,5-Dioxohexanoates

Abstract A simple and efficient method to prepare alkyl 3,5-dioxohexanoates by alcoholysis of isopropylidene (1-hydroxy-3-oxo-butylidene) malonate is described.

A Convenient Synthesis of Methyl- and Isopropyl-Benzyl Ethers Using Silver(II) Oxide as Reagent

Abstract Substituted bromomethyl- and chloromethylbenzenes and bis(bromomethyl) benzenes were directly converted, in high yields, to the corresponding methyl- and isopropyl- benzyl ethers by treatment with silver(II) oxide in methanol or isopropanol.