Regioselective syntheses of polyalkyleted cyclopentanones

Ring Expansion of Cyclobutylmethylcarbenium Ions to Cyclopentane or Cyclopentene Derivatives and Metal-Promoted Analogous Rearrangements

“…59 The synthetic applicability of this approach was further demonstrated by the synthesis of polyalkylated cyclopentanones 440 in a regioselective way using cyclobutanones 439 and carbonyl compounds 437 as starting material (Scheme 120). 165 The final step in this approach comprised a ring expansion of epoxides 439, which was achieved using lithium iodide in dichloromethane at reflux temperature to afford cyclopentanones 440 in 77À91% yield. This was the first example of a ring rearrangement of an epoxide ring bearing one or two alkyl groups.…”

“…165 The final step in this approach comprised a ring expansion of epoxides 439, which was achieved using lithium iodide in dichloromethane at reflux temperature to afford cyclopentanones 440 in 77 to 91% yield. This was the first example of a ring rearrangement of an epoxide ring bearing one or two alkyl groups.…”

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

“…Alternative methods of preparation include the addition of α-lithio selenocyclobutanes to carbonyl compounds,57,58 addition of sulfur ylides to cyclobutanones,59,60 oxidation of methylene cyclobutanes with N -bromosuccinimide in water,61 transition metal mediated epoxidations of cyclobutenes,62 and oxidation of methylene cyclobutanes with asymmetric versions of DMDO 63,64…”

Synthesis and Ring Expansions of Functionalized Spirocyclobutanones

“…Complete reversal of regioselectivity was observed when an alternative sequence was investigated. In the event, Corey−Chaykovsky epoxidation of cyclobutanone 5a , followed by direct lithium iodide induced rearrangement of the crude epoxide, provided β-spiroether 9 in high yield. 12a, This transformation, which generates the regiocomplementary cyclopentane, clearly illustrates the versatility of adducts 5 , since it now becomes evident that the regiochemistry of both carbon and oxygen insertions can be controlled at will, enabling the efficient preparation of at least four different products from a single precursor. The fact that spiroethers 5 are readily accessible from the simplest of precursors on a gram scale further emphasizes their synthetic potential.…”