171924-94-0Relevant articles and documents
Generation and cycloaddition behavior of spirocyclic carbonyl ylides. Application to the synthesis of the pterosin family of sesquiterpenes
Padwa, Albert,Curtis, Erin A.,Sandanayaka, Vincent P.
, p. 73 - 81 (1996)
The Rh(II)-catalyzed reaction of 1-acetyl-1-(diazoacetyl)cyclopropane and ethyl 3-(1-acetyl-cyclopropyl)-2-diazo-3-oxopropiolate with various dipolarophiles afforded dipolar cycloadducts in good yield. The reaction involves the formation of a rhodium carbenoid and subsequent transannular cyclization of the electrophilic carbon onto the adjacent keto group to generate a five-membered cyclic carbonyl ylide which undergoes a subsequent dipolar cycloaddition reaction. The regiochemical results encountered can be rationalized on the basis of FMC considerations. For carbonyl ylides, the HOMO dipole is dominant for reactions with electron deficient dipolarophiles, while the LUMO becomes important for cycloaddition to more electron rich species. A short synthesis of several members of the pterosin family of sesquiterpenes is described in which the key step involves a dipolar cycloaddition using a carbonyl ylide. The Rh(II)-catalyzed reaction of 1-acetyl-1-(diazoacetyl)cyclopropane with cyclopentenone afforded a dipolar cycloadduct in good yield as a 4:1 mixture of diastereomers. Treatment of the major cycloadduct with triphenylphosphonium bromide in the presence of sodium hydride gave the expected Wittig product. The reaction of this compound with acid in the presence of various solvents gave rise to several members of the pterosin family. The overall sequence of reactions can best be described as proceeding by an initial oxy-bridge ring opening followed by dehydration and a subsequent acid-catalyzed cyclopropyl ring opening. The facility of the process is undoubtedly related to the aromaticity gained in the final step.
