Diisobutylaluminum Hydride Promoted Cyclization of 1-Hydrosilyl-4-silyl-1,3-enynes to Polysubstituted Siloles

Abstract

An efficient method for preparing unsymmetrically multisubstituted siloles is described. The reaction of 1-hydrosilyl-4-silyl-1,3-enynes with diisobutylaluminum hydride (DIBAL-H) gave multisubstituted siloles in good to high yields. This method could be applied to the synthesis of benzosiloles using 2-hydrosilyl-1-(silylethynyl)benzenes as substrates. The silole formation was also promoted even by a substoichiometric amount of DIBAL-H. The reaction provides a straightforward method to prepare siloles and benzosiloles.

One-Pot Direct Synthesis of Siloles from 1-Bromo-2-silylethynylbenzenes or 1-Bromo-4-silyl-1,3-enynes

“…White solid [113 mg, 0.303 mmol, 80% yield from 1d (103 mg, 0.379 mmol)]; Mp = 78.0–79.0 °C; 1 H NMR (500 MHz, CDCl 3 ) δ 7.69 (s, 1H), 7.60 (dd, J = 8.0, 1.5 Hz, 4H), 7.43–7.42 (m, 2H), 7.37–7.34 (m, 4H), 7.30 (dd, J = 8.3, 5.0 Hz, 1H), 7.25 (dd, J = 7.5, 2.5 Hz, 1H), 7.03 (ddd, J = 8.5, 8.5, 2.5 Hz, 1H), 0.05 (s, 9H); 13 C { 1 H} NMR (125 MHz, CDCl 3 ) δ 162.8 (d, 1 J C–F = 248.8 Hz), 157.6, 146.7 (d, 4 J C–F = 2.5 Hz), 143.5, 141.6, (d, 3 J C–F = 6.3 Hz), 135.5, 132.0, 130.2, 128.1, 125.6 (d, 3 J C–F = 7.5 Hz), 119.8 (d, 2 J C–F = 21.3 Hz), 116.6 (d, 2 J C–F = 22.5 Hz), −0.1. The spectral properties of this compound were in satisfactory agreement with those previously reported …”

“…Colorless liquid [101 mg, 0.258 mmol, 78% yield from 4a (95.3 mg, 0.332 mmol)]; 1 H NMR (300 MHz, CDCl 3 ) δ 7.59–7.57 (m, 4H), 7.42–7.31 (m, 6H), 7.22 (s, 1H), 2.35–2.26 (m, 4H), 1.61–1.48 (m, 2H), 1.21–1.13 (m, 2H), 0.96 (t, J = 7.5 Hz, 3H), 0.68 (t, J = 7.5 Hz, 3H), −0.09 (s, 9H); 13 C { 1 H} NMR (125 MHz, CDCl 3 ) δ 160.4, 154.2, 141.1, 140.3, 135.5, 133.4, 129.5, 127.8, 32.3, 31.6, 23.7, 22.0, 14.4, 14.1, −0.2. The spectral properties of this compound were in satisfactory agreement with those previously reported …”

“…Colorless liquid [99.7 mg, 0.236 mmol, 48% yield from 4c (158 mg, 0.495 mmol)]; 1 H NMR (300 MHz, CDCl 3 ) δ 7.45–7.40 (m, 4H), 7.38–7.32 (m, 4H), 7.29–7.19 (m, 7H), 7.12 (s, 1H), 2.31–2.27 (m, 4H), 1.73–1.69 (m, 2H), 1.63–1.58 (m, 2H), 0.23 (s, 6H); 13 C { 1 H} NMR (125 MHz, CDCl 3 ) δ 161.7, 152.6, 139.3, 139.1, 137.7, 135.4, 134.0, 133.0, 129.5, 128.6, 127.8, 127.5, 28.0, 25.5, 22.9, 22.7, −1.4. The spectral properties of this compound were in satisfactory agreement with those previously reported …”

“…Siloles and benzosiloles have garnered increasing attention because of their specific physical and chemical properties. − Therefore, several methodologies for preparing siloles, including benzosiloles and dibenzosiloles, have been reported thus far. − Most synthetic methodologies for preparing siloles are limited to symmetrically substituted siloles bearing the same substituents, and there have been few reports on the preparation of unsymmetrically substituted siloles bearing different substituents with complete regioselectivity. To this end, we reported the synthetic methodology that enables the synthesis of benzosiloles and unsymmetrically substituted siloles bearing different substituents in good to excellent yields from starting materials 2 (Scheme (a), eq 2). , However, this method has a critical defect because it is necessary to synthesize the starting materials 2 , which are difficult to get access and purify (Scheme (a), eq 1). The corresponding silyl chlorides A are unstable under ambient atmosphere and must be transformed into hydrosilanes 2 to obtain their pure form.…”

Metal‐Catalyzed Haloalkynylation Reactions

“…show how invaluable halogenated (chlorinated) enynes are for synthetic organic chemistry. Haloenyes are crucial precursors for the synthesis of highly substituted five‐ and six‐membered heterocyclic ring systems like furans, [44] germoles, [45] phospholenes, [46] phospholes, [47] siloles, [48] thiophenes, [49] quinolines [50] and chromenes. [51] One recent example uses the Pd‐catalyzed[ 16 , 28 ] and the Au‐catalyzed bromoalkynylation [36] of alkynes for the synthesis of bromoenynes 45 , which deliver highly substituted thiophenes ( 60 and 61 ) via a chemoselective heterocyclization (Scheme 27 ).…”