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Development of Purely Organic Superconductors
Published in Toshio Naito, Functional Materials, 2019
The synthesis of EtDTET (42) is shown in Fig. 5.38. According to the literature method [100], EtDTET (42) was synthesized with an overallyield of 19% from 53. The triethyl phosphite-mediated crosscoupling reaction between 56 and 57 at 80°C afforded an EtDTET (42) yield of 36%. In this reaction, homocoupling products of 56 and 57 were also generated and it was difficult to separate EtDTET (42) from the reaction mixture because they have similar polarities. To solve the low overall yield and the difficulty in purification, an improved synthetic method was applied [220, 221]. The triethyl phosphite-mediated cross-coupling reaction was carried out between 1,3-dithiol-2-one with the phosphonate moieties 58 and 57 in toluene at 110°C and afforded a good yield of the TTF derivative (59) (82%). A few homocoupling products of 58 and 57were generated in this reaction. However, the target compound 59 was easy to separate from the reaction mixture due to the difference in polarities of 59 and the generated by-products. The Horner-Wadsworth-Emmons reaction of 59 with 3-pentanone (54) in the presence of lithium diisopropylamide (LDA) in tetrahydrofuran (THF) at −78°C gave an EtDTET (42) yield of 87%. The overall yield of the new synthetic method is successfully improved by the yield of 64% from 53.
Sonochemistry: A Versatile Approach
Published in Suresh C. Ameta, Rakshit Ameta, Garima Ameta, Sonochemistry, 2018
Grignard reagents are quite useful in organic synthesis. During conventional preparation of this reagent, one has to use the pure form of magnesium as well as distilled dry ether; whereas no prior treatment of magnesium is required and commercial sample of ether can also be used, if the reaction is carried out in the presence of ultrasound. A strong base such as lithium diisopropylamide can be obtained using lithium metal by ultrasonic exposure. This type of preparation is not possible otherwise.
Reactions between lithiated 1,3-dithiane oxides and trialkylboranes
Published in Journal of Sulfur Chemistry, 2021
Basil A. Saleh, Keith Smith, Mark C. Elliott, Gamal A. El-Hiti
Next, our attention turned to the use of less nucleophilic lithium reagents such as lithium diisopropylamide (LDA), lithium tetramethylpiperidide (LiTMP) and lithium bis(trimethylsilyl)amide (LiHDMS). First, we attempted reaction of 5 and LDA followed by protonation. Only starting material was recovered, indicating that 5 did not undergo thiophilic addition such as was seen with sec- and n-BuLi. However, when the lithiated intermediates were treated with trioctylborane the yields of 10 were still disappointingly low (Table 1; Entries 8–12). The best yield of 10 with the lithium amide reagents was 30% when the reaction was carried out with LDA (1.1 equivalents) at 0°C (Table 1; Entry 9). The use of a superbase (Schlosser’s reagent, LICKOR [36]) provided no improvement.
Novel intramolecular recyclization by cleavage and formation of C–S bonds under strongly basic conditions
Published in Journal of Sulfur Chemistry, 2022
Alexander Krivoshey, Svitlana Shishkina, Maksim Kolosov, Anatoliy Tatarets
On the other hand, in the first publication [3], it was noted (without significant details) that an additional synthetic route to compound 5 exists (Scheme 2). Under such approach, compound 10 is utilized which is in turn prepared from 2 and 4 using silyl enol ether 8 (prepared from treating 2 with TMSOTf and DIPEA) or lithium enolate 9 (prepared from treating 2 with 2.7 eq. of lithium diisopropylamide (LDA)). Later, the synthesis of compound 10via silyl enol ether 8 was reported with some experimental details [6].