A Step-Growth Approach to Metal-Capped One-Dimensional Carbon Allotropes: Syntheses of C12, C16, and C20 μ-Polyynediyl Complexes

✍ Scribed by Dr. Tamás Bartik; Dr. Berit Bartik; Dr. Monika Brady; Dr. Roman Dembinski; Prof. Dr. J. A. Gladysz

• Publisher: John Wiley and Sons
• Year: 1996
• Tongue: English
• Weight: 498 KB
• Volume: 35
• Category: Article
• ISSN: 0044-8249
• DOI: 10.1002/anie.199604141

✦ Synopsis

arnide.it"l 'That accepted. however. it is not surprising that N . Ndialkylformamides react more rapidly than higher acid amides. The procedure can be drastically simplified for formamides (entries 9 I ? in Table 1 ) and yet gives better yields (69 74%). Although with two bulky isopropyl groups the reaction required heating under reflux for 3 days, the sterically congested cyclopropyldiisopropylamine 3m was obtained from diisopropylformamide" 'I in 76 % vield. and even .I;.,%'-di-terr-butvlformainide,[t'l when treated with a threefold excess of the reagent at elevated temperatures for an extended time. gave cyclopropyldifert-butylamine (3n). the most highly congested tertiary amine known to albeit in low yield. A competition experiment disclosed that the cyclopropanation of dibenzylformamide proceeds more rapidly than that of tert-butyl acetate. Dialkylformamides can also be cyclopropanated with reagents generated from p-substituted ethylmagnesium bromides and Ti(OiPr)4, but thc 2-alkyl-1 -dialkylaminocyclopropanes 30, p are obtained with no or low diastereoselectivity only (entries 15. 16 in Table 1 ) .

General proceduie for the cyclopropmation of acid ,V..V-dialkylamidcs To ii suspension of the ~lkvlmagnesium bromide (50 mmol. 15% excess) i n T H F (200 mL. cooled to 18 -C) wasadded Ti(OiPr1, (20 mmol in 10 mL o f T H F ) under nitrogen through a steel cannula After the mixture had been stirred for 1 mic. the dialkylamide (20 mniol i n 10 niL o f T H F ) h a s ddded. a c d the mixture allowed to unrrn to 20 C. I t wds stirred for .in additional 3 h before volatile amines (with boiling points close to that of T H F a e d isopropyl alcohol together with T H F were distilled from the reaction mixture. \rithout adding water. under reduced pressure (100 Torr) into a cold t r q ) ( --18 . C ) , Addition of a solution of hydropen chloride i n ether precipi [.ired the hydrochloride of the cyclopropylamine. The crystals were collected and recrystalliied from CHCl ,;Et,O Amines with higher boiling points (cor.taining one or two benryl. isopropyl. or cyclopropyl groups i n addition to the newly formed cyclopropane ring) were isolatcd b) lirst adding saturated ammomum chloride solution ( 1 5 0 m L ) dnd wdter ( S O mL). then liltering the solution to remove the any precipitate that may have formed. and extracting i t with ether ( 3 x 50 mL1 after the solution had heer. made basic ( p H > 1 1 ) with 1 5 % sodium hydroxide solution The combined ethereal extracts were washed with saturated sodium chloride solution. dried over MgSO, o r K,CO,. and concentrated under reduced pressure (amines with C,-C,, Here first converted into nonvolatile salts with hydrogen chloride solution1 . Large amounts uere purified by distillation.

Simplified procedure for the transformation of dialkylformamides~ To a solution of didlkylformdmide ( 5 mmol) i n T H F (30 mL) was added Ti(OiPr), ( 5 . 5 mmol) and thcn at dmbient temperature wlthln 20 s a 2 85 M ethylmagnesium bromide solution in ether (12.5 mmol. 4 . 4 m L J . On warming t o 45 C the mixlure turned black. and ethane was evolved After the mixture had been stirred for a n additional 10 h. i t was ircated with I S m L of sdlurdted ammonium chloride solutior.. filtered if necessary lo remove precipitated T O , . and the filtrateextracted with ether (3 x 20 mL) The combined ethereal extracts were washed with 20 m l of sodium chloride solution. dried over K,CO,. and concentrated