Highly Efficient Catalytic Synthesis of Substituted Allenes Using Indium

Abstract

Since allenes are versatile building blocks both for organic synthesis [1] and in transition-metal-promoted carbon±carbon bond-forming reactions, [2] development of practical methods for their preparation is of great interest. Allene moieties can be prepared by alkylation of allenylmethyl halides with an appropriate carbanionic species, [1e] by S N 2'-type selective displacement of propargyl alcohol derivatives with organocopper reagents, [1e, 3] and by intramolecular regio-and stereoselective reduction of alkynes. [4] The synthesis of allenes by metal-catalyzed cross-coupling reactions is an alternative method; [5] however, some disadvantages are the inconvenient preparation of the reagents, limited substrate scope, and incompatibility of sensitive groups to the reaction conditions. [6] Recently, several reports have described the synthesis of allenes with transition metal complexes. [5] Despite this recent progress a method for the highly efficient and catalytic synthesis of substituted allenes is still needed. We have realized this goal (Scheme 1) as part of our continuing studies directed toward the development of efficient indium-mediated reactions. [7] , [8] The catalytic activity of several palladium complexes was initially examined in the reaction of 1-iodonaphthalene with allenylindium. The best results were obtained with 4 mol % [Pd(PPh 3 ) 4 ] in the presence of 3 equivalents of LiI in DMF at 100 8C under a nitrogen atmosphere (see Experimental Section), and 1-allenylnaphthalene was produced in quantitative yield (98 %) with complete regioselectivity (Table 1, entry 1). The allenylindium reagent generated in situ from the reaction of 1 equivalent of indium with 1.5 equivalents of propargyl bromide gave the best results as a coupling partner. [9] To demonstrate the efficiency and scope of the present method, we applied this catalytic system to a variety of propargyl halides and organic electrophiles. For the propargyl halides as coupling partners, the presence of various alkyl substituents at the a and g positions had little effect on either the reaction rate or the product yield (Table 1). Under the optimized conditions, treatment of iodobenzene with 3bromo-1-phenyl-1-butyne and indium gave selectively trisubstituted allene 2 in 80 % yield (entry 2). Varying the electron demand of the substituents on the arene did not diminish the efficiency and selectivity (entries 3, 7±9). It is noteworthy that protection of an oxo group and a hydroxy group on substrates is not necessary, as demonstrated by the reactions of 4iodoacetophenone (entry 5) and 3-iodophenol (entry 6), respectively. Hetero substituents turned out to be compatible with the reaction conditions (entry 10). The method worked equally well with vinyl halides (entries 11 and 12) and imidoyl bromide (entry 13). Treatment of iodophenylacetylene with allenylindium produced 3-methyl-1-phenyl-3,4-pentadien-1yne (14) in 91 % yield (entry 14). In the case of vinyl triflate, the desired product 15 was obtained in 90 % yield (entry 15). Surprisingly...

Synthesis of Cyclic Compounds Having exo-Methylene Groups through the Diels-Alder Reactions of Vinyl Allenes Obtained from Propargyl Bromide and Indium

“…Recrystallization using methylene chloride and n-hexane gave 3a (74.0 mg, 96%) as a white solid. 3, 171.3, 141.4, 135.5, 135.4, 129.6, 128.4, 128.1, 127.4, 116.2, 46.2, 40.0, 29.4, 17.0;IR (film) 2951IR (film) , 1731IR (film) , 1434IR (film) , 1241IR (film) , 1060 5,171.3,141.3,137.0,135.0,134.4,128.5,127.6,127.3,116.0,47.7,40.3,29.8,22.9,13.3;IR (film) 197.0, 196.9, 142.9, 137.1, 136.4, 135.1, 134.4, 134.3, 134.1, 133.8, 128.3, 127.7, 126.9, 126.8, 127.7, 113.7, 54.8, 47.8, 32.8, 22.1, 14.0; IR (film) 3060, 1695, 1594, 703 cm C NMR (100 MHz, CDCl 3 ) δ 170. 5, 138.1, 136.0, 135.6, 131.3, 128.4, 128.3, 127.5, 111.1, 68.0, 61.2, 21.2, 14.3, 13.8;IR (film) 2975IR (film) , 1739IR (film) , 1609IR (film) , 1465IR (film) , 1130 8, 143.4, 141.0, 136.6, 134.6, 128.2, 127.7, 126.6, 110.1, 60.4, 40.2, 35.8, 35.1, 21.9, 14.3, 14.2;IR (film) 2932IR (film) , 1732IR (film) , 1442IR (film) , 1178IR (film) , 1038 9, 143.8, 140.5, 137.9, 133.7, 128.1, 127.6, 126.4, 111.1, 60.4, 47.5, 31.1, 25.7, 22.2, 14.3, 13.9;IR (film) 2931IR (film) , 1732IR (film) , 1605IR (film) , 1443IR (film) , 1373IR (film) , 1308IR (film) , 1258IR (film) , 1155IR (film) , 1040 …”

“…4 Recently, we have demonstrated that allenylindiums generated in situ from indium and propargyl bromides are effective cross-coupling partners in palladiumcatalyzed cross-coupling reactions to produce substituted allenes in excellent yields. 5 In continuation of our studies directed toward preparative method of vinyl allenes with allenyindium, we describe herein the Diels-Alder reaction of vinyl allenes possessing 3,4-and 4,5-disubstituents and ketone group with a variety of dienophiles to give cyclic compounds having exo-methylene group (Scheme 1).First, 3-methyl-4-phenyl-1,2,4-pentatriene (1a) as vinyl allene was prepared from the reaction of α-bromostyrene with allenylindium obtained from indium and 1-bromo-2-butyne and then, the Diels-Alder reactions with dienophiles were examined to obtain cyclic compounds having exomethylene group. The results are summarized in Table 1.…”

“…4 Recently, we have demonstrated that allenylindiums generated in situ from indium and propargyl bromides are effective cross-coupling partners in palladiumcatalyzed cross-coupling reactions to produce substituted allenes in excellent yields. 5 In continuation of our studies directed toward preparative method of vinyl allenes with allenyindium, we describe herein the Diels-Alder reaction of vinyl allenes possessing 3,4-and 4,5-disubstituents and ketone group with a variety of dienophiles to give cyclic compounds having exo-methylene group (Scheme 1).…”

The chemistry of bisallenes

“…The diester 279 is also obtained when unsubstituted malonate 280 is treated with excess 2-chloro-1,3-butadiene ( 281 , chloroprene) and 2.5 equiv of sodium methoxide in the presence of Pd/DPEphos [167]. Another Pd-mediated coupling experiment, leading to a derivative of 266 involves the dibromide 282 and the aromatic haloester 283 ; the bisallene derivative 284 was obtained in 68% yield [168]. …”

Indium and Gallium-Mediated Addition Reactions

“…4) in DMF-d7 at room temperature (ratio of these two reagents; 1:6.5). 10 On the basis of this result, Chan found that the reaction of indium with propargyl bromide produced allenylindium in water. 11 But, this reaction in THF gave the mixture of allenylindium and allenylindium dibromide (eq.…”