Divergent Reactivity of Phosphorylated and Related Allenes: [4 + 2] Cycloaddition with 3,6-Diphenyltetrazine, Self-Addition Leading to Dimers and [Pd]-Complex Formation

Abstract

Phosphorus-based naphthalenes are formed by selfdimerization-cum-cyclization of α-aryl allenylphosphonates or allenylphosphine oxides using catalytic Pd(OAc) 2 in the presence of PPh 3 and Et 3 N . This reaction involves [4 + 2]-cycloaddition with the (β,γ) double bond of one allene as the dienophile; the double bonds at the α-aryl-(β′,γ′) group and (α,β)-carbons of the second allene act as the diene part. A subsequent proton shift also takes place. Upon treating allenylphosphine oxides with Pd(OAc) 2 [stoichiometry 2:1] in the presence of PPh 3 /Ag 2 CO 3 , a [Pd]complex is isolated and structurally characterized. This complex can be used as a catalyst for C−C bond-forming reactions of phosphorus-based allenes with 2-iodophenol. Densely substituted 3,6diphenylpyridazines are conveniently obtained in excellent yields by a thermally induced regioselective Inverse Electron Demand Diels−Alder (IEDDA) reaction of allenes with 3,6-diphenyltetrazine, followed by a [1,3]-H shift.

Phosphine vs DBU-Catalyzed Annulation Reactions of β′-Acetoxy Allenoates with Acyl-Tethered Benzothiazole Bisnucleophiles: (4 + 3) or (4 + 1) vs (3 + 3) Annulation

“…Yield 80.3 mg (73%), mp. 179−181 °C; 6,144.5,142.2,139.3,136.7,136.0,132.6,130.4,130.0,128.8 (2s),128.5,128.4,128.2,128.0,127.5,126.9,124.9,123.2,116.7,115.3,104.6,67.0,40.4,19.3;IR (neat): ν max 2924,1701,1624,1477,1358,1258,1198,1094,985,748 Benzyl 4-Benzoyl-3-(4-methoxyphenyl)-1-methyl-3H-benzo [4,5]thiazolo [3,2-a]pyridine-2-carboxylate (3ac). Following the general procedure, the reaction of 1a (50.7 mg, 0.20 mmol) with 2c (70.5 mg, 0.20 mmol) and DBU (6.0 μL, 0.04 mmol) afforded 3ac as a yellow solid using silica gel column chromatography (eluent:ethyl acetate:hexane 10:90).…”

“…The Journal of Organic Chemistry NMR (500 MHz, CDCl 3 ): δ 7.56 (dd, J 1 = 7.5, J 2 = 1.0 Hz, 1H), 7.44 (d,J = 9.5 Hz,2H),2H),2H),4H),3H),6.89 (dd, J 1 = 5.0, J 2 = 1.0 Hz, 1H), 6.66 (dd, J 1 = 4.5, J 2 = 3.5 Hz, 1H), 6.41 (dd, J 1 = 2.0, J 2 = 1.0 Hz, 1H), 5.80 (s, 1H), 5.25 (d,J = 12.5 Hz,1H),5.16 (d,J = 12.5 Hz,1H), 2.27 (s, 3H); 13 C{ 1 H} NMR (125 MHz, CDCl 3 ): δ 191. 5,166.4,155.8,148.3,145.1,139.2,136.7,135.9,130.4,130.0,128.7,128.3,128.1,127.6,126.9,125.8,124.9,123.9,123.4,123.2,116.8,115.2,105.4,66.9,36.8,19.1;IR (neat): ν max 2957,1703,1625,1471,1328,1214,1105,1047,882,706 5]thiazolo [3,2a]pyridine-2-carboxylate (3ah).…”

“…2,3 By contrast, the δor β′-acetoxy allenoates, by virtue of the readily detachable −OAc group, under phosphine/amine catalysis generate electrophilic diene-ammonium/phosphonium intermediates that are amenable to numerous annulation reactions. 4,5 Overall, these precursors lead to cyclization processes that may be quite different from the normal substituted allenes 6 or acetoxy allenes (allenyl acetates). 7 Thus, the Lewis base-catalyzed annulation of β′-acetoxy allenoates has been investigated by several research groups, including ours (Scheme 1a−d).…”