Eight-membered Ring Formation via Olefin Insertion into a Carbon–Carbon Single Bond

Abstract

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(4+1) vs (4+2): Catalytic Intramolecular Coupling between Cyclobutanones and Trisubstituted Allenes via C–C Activation

“…On the other hand, intermediate b can undergo β-hydrogen elimination to give enone species c . It is worthy to mention that similar sequences involving 2π-insertion followed by β-hydrogen elimination were proposed in Murakami 19b and Bower’s 20 studies. From intermediate c , either Rh–H ( d ) or Rh–C migratory insertion ( e ) followed by reductive elimination should result in the (4+1) product and regenerate the Rh I catalyst.…”

“…The reaction is expected to start with insertion of the Rh I into the cyclobutanone α C–C bond 2b,19 to give a five-membered rhodacycle ( a ) likely with the allene group coordinated to the rhodium. This is followed by migratory insertion to afford a π-allyl intermediate ( b ), 8a,9d,10a which can undergo at least two different pathways.…”

Fused‐Ring Formation by an Intramolecular “Cut‐and‐Sew” Reaction between Cyclobutanones and Alkynes

“…[2] However,u sing such as trategy to assemble fused-ring systems is still challenging (Scheme 1b). [3] Them ain difficulty associated with the fused-ring formation arises from the need for CÀCc leavage and coupling at the more sterically hindered C2 (proximal) position (Scheme 2a); the selectivity typically favors the less bulky C4 (distal) position (Scheme 2b). [2g] In addition, decarbonylation of cyclobutanones to form the corresponding cyclopropane byproduct is always amajor competing pathway.…”

Synthesis of unusually strained spiroheterocyclic ring systems and their exploits in synthesis

“…An example is the rhodium-catalyzed synthesis of an eight-membered ring developed by Murakami (Scheme 14). 32 The o -styryl-cyclobutanone 50 was synthesized utilizing Trost’s cyclopropyl sulfoxonium ylide 24 procedure to generate oxaspiro[2.2]pentane 49 ,25 which was subsequently rearranged under protic conditions to yield the desired cyclobutanone 50 . Cyclobutenone 50 was transformed to octanone 51 via olefin insertion and subsequent hydrogenation.…”