Polyspirane, 14. — Umlagerungskaskaden, 9. Fünffache Cyclobutylmethyl‐Cyclopentyl‐Umlagerung an einem Pentaspiro[3.0.3.0.3.0.3.0.3.1]henicosanol — Eine Schlüsselsequenz zur Synthese des [6.5]Coronans

Abstract

Das Pentaspirohenicosanol 6 reagiert mit Thionylchlorid in Pyridin unter WntTacher Cyclobutylmethyl-Cyclopentyl-Umlagerung zu einem all-cis-anellierten hexacyclischen Olefin 17, dessen Struktur und Konfiguration iiber eine Kristallstrukturanalyse eines hiervon abgeleiteten Epoxids 18 gekllrt wurde. Die Umlagerung ist konformativ kontrolliert und eine Synthese des [6.5]Coronans (5) geeignet. Der A k o h o l 6 wurde aus dem Trion 7 iiber eine Folge aus selektiver Dicyclopropylidenierung, erschbpfender Epoxydierung, Oxaspiropentan-Cyclobutanon-Urnlagerung, selektiver Reduktion und Addition von Methyllithium erhalten (7--+8--r10-+ 11+1246). Polycyclische Kohlenwasserstoffe, bei denen ein Zentralring der Kantenzahl m ( m = 4,6,8 ...) mit m peripheren Ringen der Kantenzahl n ( n = 3,4,5 ...) so verkniipft ist, dal3 jede Kante des Zentralringes zugleich Kante eines peripheren Ringes ist ([mnlCoronane). waren bisher nicht bekannt. Diese Verbindungen besitzen eine ungewohnliche Topologie und lassen interessante chemische und physikalisch-chemische Eigenschaften erwarten. Dies gilt insbesondere fur solche Systeme, die einen zentralen Sechsring enthalten. Beispiele sind C6.41Coronan ( 2 ) und C6.51Coronan (5). Schema 1 nu 1 2 3 4 5 6 -Cpscpde Rearrangemeate, 9Is? -Fivefold Cycloktylmetbyl-Cyclopeatyl Rearrangement in a Peataqiro-[3.0.3.0.3.0.3.0.3.1]~1 -A Key Sqoeoce for the SptBesis of [65]CoroanneThe pentaspirohenicosano16 reacts with thionyl chloride in pyri d h e to give, in a fivefold cyclobutylmethyl-cyclopentyl rearrangement, the all-cis annulated hexacyclic oleGn 17, whose structure and conformation was established by X-ray analysis of a n epoxide 18 derived therefrom. The rearrangement is conformationally controlled and suitable for the synthesis of [6.5]coronane (5). The 121~). Chem. Ber. 121, 525-531 (1988) VCH Verlagsgesellschaft mbH, D-6940 Weinheim, 1988 ooO9-2940/88/0303-0525 S 02.50/0

The Application of Cyclobutane Derivatives in Organic Synthesis

“…A striking example of a cationic cascade reaction is the 5-fold cyclobutylmethyl−cyclopentyl rearrangement of the pentaspirohenicosanol 241 to the all- cis - annelated precursor 242 of [6.5]coronane (83% yield) reported by Fitjer et al This reaction was speculated to proceed with conformational control starting from an initially formed chlorosulfite. Fitjer and Quabeck had previously reported the formation of [4.5]coronane in 40% yield by means of a comparable cationic cascade rearrangement followed by a photolytic decarbonylation …”

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

“…A final example of a cationic cascade reaction of this type of rearrangements included the fivefold cyclobutylmethyl to cyclopentyl rearrangement of pentaspirohenicosanol 607 to the all- cis annelated precursor 608 of [6.5]coronane (Scheme ) . The reaction was speculated to proceed with conformational control, starting from an initially formed chlorosulfite.…”

“…A final example of a cationic cascade reaction of this type of rearrangements included the five-fold cyclobutylmethyl to cyclopentyl rearrangement of pentaspirohenicosanol 607 to the all-cis annelated precursor 608 of [6.5]coronane (Scheme 164). 235 The reaction was speculated to proceed with conformational control, starting from an initially formed chlorosulfite. When pentaspirohenicosanol 607 was treated with five equiv of thionyl chloride in pyridine, the corresponding hexacyclohenicos-16-ene 608 was obtained in 83% yield.…”

Calixrotanes: Calixarenes Incorporating Spiro‐Linked Cyclopropyl Groups

“…The formal introduction of spirocyclopropyl groups into the cyclohexyl ring increases its rigidity, and the barrier of chair‐to chair inversion for [6]rotane is 21.3 kcal mol −1 . This barrier is significantly larger than that for cyclohexane, and therefore in solution at room temperature, the chair conformation of the central cyclohexane ring is frozen on the NMR timescale . Rotanes have served as the inspiration for the synthesis of macrocycles incorporating spirocyclopropyl units .…”