Base catalysed intramolecular cycloadditions of 3-phenylprop-2-ynyl allyl ethers and 4-methylpent-4-en-2-ynyl prop-2-ynyl ethers

Abstract

Der ungesättigte Äther (I) liefert bei Behandlung mit überschüssigem Kaliumtert.‐butylat die Cyclisierungsprodukte (II) und (III), die zu (IV) hydriert werden.

On the Mechanism of Intramolecular Cyclization of Dialkyl(2-propynyl)[3-alkenyl(or aryl)-2-propynyl]-ammonium Salts

“…Scheme 3 is consistent with published data on cyclization of acetylenic compounds [16][17][18][19][20]. For example, base-catalyzed intramolecular cyclization of compounds with the general formula X(CH 2 C≡CC 6 H 5 ) 2 (X = CH 2 , S, NCH 3 , O), as well as of allyl and 2-propynyl ethers derived from 3-isopropenyl-2-propynyl and 3-phenyl-2-propynyl alcohols, was presumed to be preceded by isomerization into the corresponding α-allenyl derivative [16][17][18].With the goal of establishing the true mechanism of the cyclization, Babayan and co-workers previously performed kinetic studies using UV spectroscopy [8][9][10][11][12][13][14][15]. However, this method did not allow the authors to detect formation of intermediate species, in N OH -N H A N H B H OH b a N Scheme 2.…”

The intramolecular Diels-Alder reaction

“…45 More specific use of the reaction was made in a synthesis of a thujopsene derivative useful in fragrances. Thus, cyclization of ketone 65 proceeded readily to give a mixture of 66a and 66b. That these were indeed the kinetic products was shown by equilibrium of either isomer to the same 3:1 mixture.46 Khusimone, a norsequiterpene component of Vetiver oil, has been prepared by an IMDA of intermediate 67 to 68a and 68b.…”

“…C skeleton Rj = Rj = R3 = R4 = H; Rs = O; similar to C but with trans (=) C' Rj = Rj = Rj = R4 = H; Rs = NH; R6 = CO; R, = C6H5133b. skeleton similar to C but with trans (=) R, = Rj = R3 = R4 = H; 55% (i), 28 (ii) (c) 55 °C, KO-t-Bu (d) 3 in bridge; adduct forms after isomerization of triple bond to allene system (a)65 (b) 52% (i), 30% (ii) (c) 55 °C, KO-t-Bu (d) 3 in bridge; adduct forms after isomerization of triple bond to allene system (h i b i t e d .…”

The chemistry of bisallenes

“…An analogous mechanism can also be proposed for the isomerization of the vinyl-substituted bispropargyl ether 552 , which has been studied by Ollis et al (Scheme 122) [283–285]. In this case the initial isomerization leads to the monoallenes 553 , which can either undergo a second acetylene-to-allene rearrangement and provide the bisallenyl ether 554 or participate in a Diels–Alder addition to 556 .…”