C3 —> C5 ring expansions

It is noteworthy that, contrary to 1-trimethylsiloxyvinylcyclopropanes which readily undergo thermal C3 - C5 ring expansion (vide infra, Sect. 5.5), the O-silylated 1-ethy-nylcyclopropanols 9 were recovered unchanged, on heating to 600 °C 28). 

The spiro compound 347 constitutes the basic carbon framework found in sesquiterpenes of the spirovetivane and acorane class 184), which have been the target of many syntheses 185). The thermal C3 -> C5 ring expansion 111 -> 347 was of... 

The accessibility to 2,3-disubstituted — and 4,5-disubstituted 2-cyclopentanones by this thermal C3 -< C5 ring expansion has been illustrated by the syntheses of dihydrojasmone 92), cis-Jasmone 92) and dicranenone A188). 

Metal-promoted vinylcyclopropane C3 - C5 ring expansions have been reported. Thus, ethyl 2-methoxy-2-vinylcyclopropanecarboxylate 393 rearranged to a 2 1 mixture of 3-methoxy-2-cyclopentenecarboxylate 396 and 3-methoxy-3-cyclopentene-carboxylate 397 on heating at 160 °C in the presence of catalytic amounts of copper bronze or copper(I) chloride in contrast, platinum and rhodium complexes catalyzed... 

Formally a cyclopropane is a small ring with double bond character which, more specifically, can undergo ring-opening, C3 - C4 and C3 - C5 ring expansions and is also involved in the C4 - C3 ring contraction of four-membered cyclic systems. This chapter is concerned with such rearrangements. 

The solvolysis of spiro[2.n]alkan-4-ol derivatives leads to ring enlargement products. In particular, solvolysis of spiro[2.3]hexyl-4-(3, 5 -dinitrobenzoates) (ODNB) (237) in 80% aqueous acetone gives a mixture of five-membered ring compounds derived from C3 - C5 ring expansion (equation 156) . 

It should be realized that the five-membered ring products stem from the subsequent C3 -> C5 ring expansion of the 2-methylenevinylcyclopropane formed by the ring contraction (cf. Section IV.A. 1, equation 141). 

Thus, dihydrojasmone, " cw-jasmone, a precursor of methylenomycine B, dicran-enone A, a member of a new class of fatty acids having a cyclopentenone ring structurally similar to prostanoids and jasmonoids, have been synthesized from the 1-hydroxycyclopro-panecarbaldehyde derivatives, either via thermal C3 Cj or acid induced C3 -> C4 C5 ring expansions. ... 

---