Stereocontrolled double ring expansion of fused allylidenecyclopropanes. A novel route to hydroazulenes and other fused bicyclic systems

Strain-Induced Transformations of Bicyclo[3.1.0]hex-1-enes

“…Diradical 69a can be cyclized through two competing pathways (path a or path b), depending on the rotation of the C-C bond (rotation a or rotation b). 43,44 Two opposite steric elements play a key role in determining the reaction pathway. Diradical closure via path a introduces H x /H strain in TSa, which is less penalizing compared to H x /CH 3 strain in TSb in path b.…”

Functionalised organolithium compounds by sulfur–lithium exchange

“…20 Allylidenecyclopropanes, which were prepared following the previously reported methodology (using a,b-unsaturated aldehydes as electrophiles), showed synthetic interest because they underwent thermal rearrangement either in a sealed tube or in a flash vacuum pyrolysis apparatus to give among other products cyclopentenocyclohexenes or -cycloheptenes (hydroazulenes). 21,22 Scheme 5 The lithium enolate 30, formed by the addition of tris-(pheny1thio)methyllithium to 2-cyclohexen-1-one (29), reacted with sec-butyllithium at À78 1C to form a highly stabilised enolate thioacetal dianion 31, which can be considered an a-sulfurfunctionalised organolithium compound. In this case, sec-butyllithium was used as the lithiating reagents instead of lithium metal in the presence of an arene.…”

Short Access to the Aromadendrane Family: Highly Efficient Stereocontrolled Total Synthesis of (±)‐Cyclocolorenone and (±)‐α‐Gurjunene

“…One of them uses the photochemical rearrangement outlined by Barton, [9] and another one is based on the thermolysis of an allylidenecyclopropane. [10] Nicholas and co-workers more recently applied their cyclopentannulation reaction to this class of compounds and synthesized (Ϯ)-cyclocolorenone (2) over 10 steps in 8.9 % overall yield from tropone.…”