The Phenylsulfonyl Group as anendo Stereochemical Controller in Intramolecular Pauson–Khand Reactions of 3-Oxygenated 1,6-Enynes

Abstract

Unlike the usual exo‐selective Pauson–Khand cyclization of allylic‐substituted 1,6‐enynes, the reaction of 1,6‐enynes with γ‐oxygenated α,β‐unsaturated sulfone structures occurs with high endo stereoselectivity. As the starting enynes are available in enantiopure form and the sulfonyl group can be easily eliminated, this procedure constitutes a stereocomplementary approach to the asymmetric synthesis of bicyclo[3.3.0]oct‐1‐en‐3‐ones [Eq. (1)].

Total Synthesis of Valerenic Acid, a Potent GABAA Receptor Modulator

“…Our synthesis (Scheme 3) started with readily available racemic 3-OTBS-oct-1-en-6-yne (7), 12 which smoothly underwent RCM to cyclopentene 12 with Grubbs' first generation catalyst, if the reaction was carried out under an ethylene atmosphere (Mori's conditions). 13 Several other conditions such as using an argon atmosphere instead of ethylene or PtCl 2 as catalyst led to no conversion or decomposition.…”

Unusual Palladium-Catalyzed Cascade Arylation ofα,β-Unsaturated Phenyl Sulfones under Heck Reaction Conditions

“…In our research into the use of substituted vinyl sulfones in stereoselective synthesis,4 we envisaged that acyclic β , β ′‐disubstituted‐ α , β ‐unsaturated sulfones could be stereoselectively prepared by simple Heck arylation of α , β ‐unsaturated sulfones through the seemingly evident syn ‐carbopalladation/ syn ‐ β ‐hydrogen elimination pathway 5. However, we describe herein that the palladium‐catalyzed reaction of trans ‐ α , β ‐unsaturated phenyl sulfones with excess iodobenzene/Ag 2 CO 3 proceeds by an intermolecular four‐component cascade reaction to give 1‐phenyl‐9‐phenylsulfonyl‐9,10‐dihydrophenanthrenes in which four C−C bonds are formed in a single step.…”

Untitled

“…For example, 110 ( > 98% ee) gave endo-111 in 72% yield and > 96% ee, Scheme 30. 47 Some progress has been made in the development of chiral control elements to render the PKR enantioselective. In one case a bidentate P,S-ligand (PuPHOS, 112) proved highly selective.…”