Photochemical Myers−Saito and C²−C⁶ Cyclizations of Enyne−Allenes:  Direct Detection of Intermediates in Solution

Abstract

Several examples of the photochemical Myers-Saito and C2-C6 cyclization of enyne-allenes are described. The presence of a triplet sensitizing unit at the allene terminus and laser flash photolysis results suggest that the cyclization proceeds along the triplet manifold. An intermediate with tau = 33 +/- 5 mus was tentatively assigned to a singlet biradical.

10.1007/s11176-008-2012-z

“…Like other enyne3allenes having bulky groups, thermal cyclization of compounds 78a378e leads to C 2 3C 6 bonding products 79a379e [57] (Scheme 23). All attempts to effect photocyclization of compound 78a in hexane or toluene were unsuccessful because of the low triplet energy of bromonaphthalene (E T = 59 kcal mol 31 ), so that the use of a stronger internal sensitizer was necessary [56].…”

“…All attempts to effect photocyclization of compound 78a in hexane or toluene were unsuccessful because of the low triplet energy of bromonaphthalene (E T = 59 kcal mol 31 ), so that the use of a stronger internal sensitizer was necessary [56]. in fact, irradiation of 78b (R = 4-biphenylyl, E T = 65 kcal mol 31 ) in toluene at l 300 nm in the presence of cyclohexa-1,4diene resulted in the formation of both C 2 3C 6 and Myers3Saito cyclization products 80 (12%) and 81 (24%) [57] (Scheme 24). Irradiation of enyne3allen 78c at l 300 nm gave compound 79c, and product 79d was obtained in 32% yield from compound 78d under analogous conditions.…”

Synthesis of novel polycyclic aromatic compounds via cascade cyclizations of benzannulated enyne -allenes

“…Myers−Saito cyclization reaction and Schmittel cyclization reaction could be induced either thermally or photochemically. 13…”

“…13 C NMR δ 143.6,132.2,132.0,131.7,129.6,128.4,128.3,128.2,127.9,125.8,124.6,124.3,122.9,93.4,87.9,86.5,80.2,57.4 13 C NMR δ 144.6,132.4,132.1,131.7,129.7,128.41,128.38,128.3,127.9,126.1,124.8,124.7,122.9,93.4,90.9,88.0,85.9,81.8,56.3,25.8,15.7. 2.02 (6 H, s); 13 C NMR δ 145. 9, 143.8, 142.1, 139.2, 138.6, 134.9, 134.7, 131.8, 130.1, 128.9, 127.6, 126.9, 126.5, 126.4, 124.9, 123.7, 123.4, 51.1, 33.8, 23.3 6, 136.3 133.7, 131.27, 131.23, 130.1, 129.60, 129.57, 128.7, 128.6, 128.18, 128.05, 127.9, 126.98, 126.92, 126.90, 126.6, 126.3, 125.9.…”

“…Propargylic Alcohol 172a. The same procedure was repeated as described for 165a except that 0.126 g of 2,2-dimethylpropiophenone (147, 0.78 mmol) was treated with the lithium acetylide, prepared from 0.127 g of tetraacetylene 171a (0.39 mmol) and 0.49 mL of a 2.0 M solution of lithium diisopropylamide (0.98 mmol) in THF/n-heptane, to afford 0.220 g of 172a (0.34 mmol, 87%) as a white solid: IR 3371, 2212, 1598, 1498 cm −1 ; 1 H NMR δ 7.75 (1H, s), 7.74-7.71 (4 H, m), 7.63 (1 H, s), 7.47-7.43 (4 H, m), 7.36-7.31 (6 H, m), 7.28-7.24 (6 H, m), 2.42 (2 H, s), 1.09 (18 H,s); 13 C NMR δ 141. 7, 135.67, 135.61, 131.8, 128.7, 128.3, 127.7, 127.4, 127.1, 125.5, 124.5, 122.6, 98.3, 95.1, 87.3, 83.6, 79.6, 39.8, 25.6.…”