Stereochemistry of an Ene Reaction Involving 1,7‐Dienes; Bicyclo[3.3.1]nonanes from (3‐Cyclohexenyl)diallylcarbinols

Abstract

Summary(3-Cyclohexenyl)diallylcarbinols undergo a thermal retro -ene reaction to give crotonylcyclohexenes at ca. 200". A side-reaction is an ene reaction to give bicyclo[3.3. llnonanes. These become the main products above 300". The stereochemistry of 2-allyl-1,4,6-trimethylbicyclo[3.3.l]-6-nonen-2-ols and related compounds is discussed, and a case is described in which the ally1 group is not freely rotating.Introduction. -One route for the preparation of the useful perfume substances 1-(1,3-dimethyl-3-cyclohexenyl)-2-buten-1-one (1) and 1-(1,4-dimethyl-3-cyclohexenylj-2-buten-1-one (2) involves the reaction of allylmagnesium chloride with the products 3, 4, of a Diels-Alder reaction between isoprene and methyl methacrylate [l] (Scheme I ) . The initial compounds formed are the diallyl compounds 5 and 6, and

Synthesis of (E)‐1‐Propenyl Ketones from Carboxylic Esters and Carboxamides by Use of Mixed Organolithium‐Magnesium Reagents. Synthesis of α‐Damascone, β‐Damascone, and β‐Damascenone

“…With the goal being a direct approach to the precious rose ketones 4-6 [6] as well as the perfumistically interesting ketone 10 [7], we required an efficient method for converting a carboxylic esters or carboxamide into a (E)-1-propenyl ketone. We reasoned that for substrate esters or amides i with a low tendency to enolize, the presence of a strong external base would protect the intermediate 2-propenyl ketone v from further reaction (to vi) by rapid deprotonation into its enolate vii (Scheme 2).…”

“…To gain more insight into the course of this reaction, we selected the ester 8 [7] [13] and the amide 9, which bear no H-atom in the a-position, as test substrates (Scheme 4 ) .…”