Synthesis of (−)-β conhydrine and analogues using N-Boc-2-acyl oxazolidine methodology and ring closing metathesis

Recent applications of the Wittig reaction in alkaloid synthesis

The Wittig reaction is the chemical reaction of an aldehyde or ketone with a triphenyl phosphonium ylide (the Wittig reagent) to afford an alkene and triphenylphosphine oxide. Noteworthy, this reaction results in the synthesis of alkenes in a selective and predictable fashion. Thus, it became as one of the keystone of synthetic organic chemistry, especially in the total synthesis of natural products, where the selectivity of a reaction is paramount of importance. A literature survey disclosed the existence of vast numbers of related reports and comprehensive reviews on the applications of this important name reaction in the total synthesis of natural products. However, the aim of this chapter is to underscore, the applications of the Wittig reaction in the total synthesis of one the most important and prevalent classes of natural products, the alkaloids, especially those showing important and diverse biological activities.

Asymmetric synthesis of delta-substituted alpha,beta-unsaturated delta-lactams by ring closing metathesis of enantiomerically pure N-acryloyl-homoallylic amines

Optically pure secondary homoallylic amines, obtained by highly diastereoselective addition of allylmetal reagents to imines derived from chiral amines, were N-dealkylated, and the primary amines were converted to N-acryloyl amides. Then, ring closing metathesis gave delta-substituted delta-lactams in good overall yields.

Relative rate profile for ring-closing metathesis of a series of 1-substituted 1,7-octadienes as promoted by a 4,5-dihydroimidazol-2-ylidene-coordinated ruthenium catalyst

[reaction: see text] This report details the kinetic responses of nine compounds of type 6 to ring-closing metathesis as promoted by 2 to give the identical product 7. The experimental observations have been subjected to Hammett analysis. The rho value for the composite aromatic derivatives (R = p-XC(6)H(4)-) differs from that of the aliphatic series, although both are negative because electron-donating groups accelerate the reaction.

Enamide-olefin ring-closing metathesis

[reaction: see text] The first examples of ring-closing metathesis reactions of olefin-containing enamides using ruthenium-based catalysts have been demonstrated. A preliminary investigation into the scope and limitations, leading to protected five- and six-membered cyclic enamides, will be presented.