Ketenes. V. Reactions of Ketenes with Dienes and Olefins¹

Pericyclic Reactions of Cumulenes* *This chapter is dedicated to Professor R. B. Woodward on the occasion of his 60th birthday.

“…Thus, eis-and trans-enol ethers were shown (Huisgen et al, 1964Martin et al, 1965) to add in a cis-stereospecific fashion to diphenyl and dimethyl ketenes. Thus, eis-and trans-enol ethers were shown (Huisgen et al, 1964Martin et al, 1965) to add in a cis-stereospecific fashion to diphenyl and dimethyl ketenes.…”

“…The product resulting from the cycloaddition of alienes with ketenes is, in most cases, the 2-methylenecyclobutanone adduct (Martin et al, 1965;Bertrand et al, 1968aBertrand et al, , 1975a. The reaction is thus generally regio-and perispecific.…”

Synthesis of the hexacyclic triterpene core of the jujuboside saponins via tandem Wolff rearrangement–intramolecular ketene hetero-Diels–Alder reaction

“…35 In contrast, [4+2] cycloadditions involving either the C=C or C=O bonds of ketenes are rare and usually regarded as exceptions. 36–54…”

Formation of tricyclo[6.3.0.02,5]undecane derivatives during attempts to make the rumphellatin A–C oxacarbon skeleton

“…[7][8][9][10][11][12][13][14][15][16][17][18][19][20] This competing reactivity could conceivably become a problem, but that appeared first not to be the case; when the compound was reacted with dimethylketene generated in situ in acetonitrile, the allene was attacked regioselectively in a head-to-tail fashion and afforded (4Z,8E)-11,11-dimethylbicyclo[7.2.0]undeca-4,8-dien-10-one (2) in 40% isolated yield. It is interesting to note that when the solvent was changed to hexane, which has been used frequently by Brady et al in similar reactions, 16 no reaction occurred.…”