Non-metal-templated approaches to bis(borane) derivatives of macrocyclic dibridgehead diphosphines via alkene metathesis

• Published in: Beilstein journal of organic chemistry 2018-09, Vol.14 (1), p.2354-2365
• Main Authors: Fiedler, Tobias, Barbasiewicz, Michał, Stollenz, Michael, Gladysz, John A
• Format: Article
• Language: English
• Subjects: alkene metathesis; Bromination; Chemistry; Column chromatography; crystal structures; Dichloromethane; Full Research Paper; homeomorphic isomerization; hydrogenation; in/out isomers; Ligands; metathesis; phosphine boranes; Phosphorus; Stereoisomers
• ISSN: 1860-5397; 2195-951X; 1860-5397
• DOI: 10.3762/bjoc.14.211

Two routes to the title compounds are evaluated. First, a ca. 0.01 M CH Cl solution of H B·P((CH ) CH=CH ) ( ·BH ) is treated with 5 mol % of Grubbs' first generation catalyst (0 °C to reflux), followed by H (5 bar) and Wilkinson's catalyst (55 °C). Column chromatography affords H B·P( C H ) (1%), H B· ((CH ) H )( -C H ) (8%; see text for tie bars that indicate additional phosphorus-carbon linkages, which are coded in the abstract with italics), H B· ((CH ) H )((CH ) ) ((CH ) H )·BH ( ·2BH , 10%), -H B·P((CH ) ) P·BH ( - ·2BH , 4%) and the stereoisomer ( / )- ·2BH (2%). Four of these structures are verified by independent syntheses. Second, 1,14-tetradecanedioic acid is converted (reduction, bromination, Arbuzov reaction, LiAlH ) to H P((CH ) )PH ( ; 76% overall yield). The reaction with H B·SMe gives ·2BH , which is treated with -BuLi (4.4 equiv) and Br(CH ) CH=CH (4.0 equiv) to afford the tetraalkenyl precursor (H C=CH(CH ) ) (H B)P((CH ) )P(BH )((CH ) CH=CH ) ( ·2BH ; 18%). Alternative approaches to ·2BH (e.g., via ) were unsuccessful. An analogous metathesis/hydrogenation/chromatography sequence with ·2BH (0.0010 M in CH Cl ) gives ·2BH (5%), - ·2BH (6%), and ( / )- ·2BH (7%). Despite the doubled yield of ·2BH , the longer synthesis of ·2BH vs ·BH renders the two routes a toss-up; neither compares favorably with precious metal templated syntheses.