A variety of systems were considered that differed in the nature of the phosphine (PMe3 or PPh3) and of the spectator ligand (chloride, methyl or hydride).
Terpene synthases generate terpenes employing beautiful and rich carbocation chemistry, including highly specific ring formations, hydride, proton, methyl, and methylene migrations, followed by reaction quenching.
(83) The protosterol cation converts to lanosterol 11 by elimination of the 9α-H atom (originally the 9βH of the protosteroid cation), which requires nuclear rearrangements that involve a series of 1,2-shifts of hydride and methyl groups in an antiparallel manner coupled to quenching of the positive charge at C20.
Most likely, the ligand cation electronegativity affects the magnitude of the rate-determining surface reaction step, krds, via its influence on the ability of the active metal cation to decompose the adsorbed methoxylated surface intermediates by hydride abstraction of methyl hydrogen.
Most convenient was to buffer the reaction with a weak base (Ph2NH), whose conjugate acid could promote the fragmentation of commercially available trityl methyl ether into the active hydride abstractor (and MeOH).
Terpene cyclases play a key role in the biosynthetic processes of terpenoids, because they yield structurally and stereochemically diverse ring skeletons in the reaction cascade, which involves ionization, hydride shifts, deprotonation, protonation, methyl migration, and hydroxylation.
Finally, introduction of a Cbz group followed by reduction of 25 with lithium aluminium hydride gave the N-methyl amine 26.
The extended ether linker compounds 28– 34 were synthesised from compound 5 and the corresponding pyridyl methyl alcohol under basic conditions using sodium hydride in a tetrahydrofuran (THF) solution (Scheme 3).
After deprotonation of 17 with sodium hydride and heating the resulting anion with methyl iodide, the N-methyl derivative 18 a was obtained in high yield.
Sodium hydride (NaH) 60% in oil, 2-bromoethyl methyl ether, 1, 2-dibromoethane and 4- phenylazo) phenol, and anhydrous tetrahydrofuran (THF) were purchased from Tokyo Chemical Industry Co., Ltd.
