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Recent Developments in Bisdiborane Chemistry: B—C—B, B—C—C—B, B—C=C—B and B—CC—B Compounds

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Recent Developments in Bisdiborane Chemistry: B—C—B, B—C—C—B, B—C=C—B and B—CC—B Compounds See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/264295611 Recent Developments in Bisdiborane Chemistry: B—C—B, B—C—C—B, B—C=C—B and B—CC—B Compounds Article in ChemInform · August 2003 DOI: 10.1002/chin.200332254 CITATIONS READS 0 28 3 authors, including: Valery Dembitsky Hijazi Abu Ali Institute of Marine Biology Birzeit University 341 PUBLICATIONS 4,825 CITATIONS 58 PUBLICATIONS 331 CITATIONS SEE PROFILE SEE PROFILE Some of the authors of this publication are also working on these related projects: Antitumour natural metabolites isolated from fungi, plant and microorganisms View project Plasmalogens of marine invertebrates, functions and structures View project All content following this page was uploaded by Valery Dembitsky on 28 January 2015. The user has requested enhancement of the downloaded file. All in-text references underlined in blue are added to the original document FADA - Birzeit University and are linked to publications on ResearchGate, letting you access and read them immediately. provided by View metadata, citation and similar papers at core.ac.uk CORE brought to you by APPLIED ORGANOMETALLIC CHEMISTRY Appl. Organometal. Chem. 2003; 17: 327–345 Main Group Metal Compounds Published online in Wiley InterScience (www.interscience.wiley.com). DOI:10.1002/aoc.430 Review Recent developments in bisdiborane chemistry: B–C–B, B–C–C–B, B–C C–B and B–C C–B compounds† Valery M. Dembitsky, Hijazi Abu Ali and Morris Srebnik* Department of Medicinal Chemistry & Natural Products, School of Pharmacy, PO Box 12065, Hebrew University of Jerusalem, Jerusalem 91120, Israel Received 18 November 2002; Revised 27 November 2002; Accepted 13 January 2003 An overview of the development of new strategies in organic synthesis with a minimum of chemical steps is becoming increasingly necessary for the efficient assembly of complex molecular structures. Therefore, the combination of multiple reactions in a single operation represents a particularly efficient approach. Among these strategies, the synthesis and reactivity of bisdiboranes has never been reviewed although its popularity for the synthesis of complex architectural molecules has been steadily increasing during the last decade. This review is intended to highlight the use of partly geminated boranes (B–C–B), and also bisdiborane reagents (B–C–C–B, B–C C–B, B–C C–B). Copyright 2003 John Wiley & Sons, Ltd. KEYWORDS: bisdiborane; geminated boranes; tetraorganodiborane; bis(pinacolato) diborane(4); bis(catecholato) diborane(4); diazoalkanes; insertions; hydroboration; dihydroboration; carbenoids; bis(boryl)alkenes; vinylphosphonates; 1-alkynylboronates; diboration; thermolysis 5,6 INTRODUCTION are present such as amido (NR2)oralkoxy(OR). More recently, as part of the interest in the oxidative addition Bisdiborane derivatives are an important class of compounds chemistry of the B–B bond and metal-catalyzed diborations in boron chemistry. The addition of diboranes (X B–BX )to 2 2 of alkenes7–10 and alkynes,11–16 synthesis of stable, crystalline unsaturated hydrocarbons, first discovered by Schlesinger bis(pinacolato) and bis(catecholato) diborane(4) derivatives and coworkers in 1954,1 is an attractive and straightfor- have been reported.17,18 ward method to introduce two boryl units into organic 2–4 The development of new strategies in organic synthesis molecules. Diborane itself, B2H4,isstableonlywhencom- with a minimum of chemical steps is becoming increasingly plexed by Lewis base ligands such as amines or phosphines. = important for the efficient assembly of complex molecular Although the tetrahalides, B2X4 (X F, Cl, Br, I), have a structures.19,20 The combination of multiple reactions in a reasonably well-established chemistry, they suffer from low single operation represents a particularly efficient approach. thermal stability (with the exception of B2F4) and prepara- Among these strategies,21 geminated organobismetallic tive difficulties. Tetraorganodiborane compounds, B2R4,are stable only when substituted with sterically demanding R derivatives (1,1-bis anions) are becoming increasingly useful.22 During the past decades considerable efforts have groups such as t-Bu, CH2 –t-Bu, and mesityl. The most sta- ble derivatives are those in which good π-donor groups been made to find new routes for the preparation of geminated sp2 organobismetallic derivatives and for their selective reactions with several electrophiles.22,23 *Correspondence to: Morris Srebnik, Department of Medicinal Chemistry & Natural Products, School of Pharmacy, PO Box 12065, This review will concentrate primarily on features of the Hebrew University of Jerusalem, Jerusalem 91120, Israel. chemistry of diborane compounds with particular structures: E-mail: [email protected] B–C–B,B–C–C–B,B–C C–B,andB–C C–B. We will also †Dedicated to Professor Thomas P. Fehlner on the occasion of his 65th birthday, in recognition of his outstanding contributions to survey some of the chemistry of organoboron compounds organometallic and inorganic chemistry. derived from diborane precursors. Copyright 2003 John Wiley & Sons, Ltd. 328 V. M. Dembitsky, H. Abu Ali and M. Srebnik Main Group Metal Compounds OO O O Pt(PPh3)4 B B + CH N B CH B 2 2 ° 2 O O Et2O, 0 C O O 1 Scheme 1. O R1 O FORMATION OF B–C–B COMPOUNDS OO R1 Pt(PPh3)4 B B + C = N B C B 2 toluene, O O R2 O O Bisdiborane, BCB, compounds are usually prepared 80 °C R2 by double hydroboration of terminal alkynes with 6 dialkylboranes.24–26 They are interesting precursors to gem- bimetallics such as BCLi27–30 and BCMgX.31 Recently, we Me reported that the parent compound (pinacolato)2BCH2B O O O (1) can be prepared in high yield by reaction of B C B O O O O bis(pinacolato)diborane(4) with diazomethane (Scheme 1).32 Me B C B O O This reaction gave good results and had not been described 8a, 76% Me before. 8b, 75% Insertions into (R N) B–B(NR ) ,whereR= Me, Et, n-Pr, O 2 2 2 2 B O O were not successful. Two mechanisms for the insertion are O B C B C possible: (a) addition/1,2-migration to and from boron as O O O in the Hooz reaction33–35 or (b) oxidative addition of B–B B O to a Platinum(0) complex, insertion of CH2 into the Pt-B bond, migration, and reductive elimination.36 Alternatively, 8c, 78% 8d, 75% formation of 1 from (pin)BCH2I by coupling with metals has been reported.32 Reflux of 1 and 3 with HCl gave the stable Scheme 3. boronic acids 4 and 5 respectively (Scheme 2). Novel C1-bridged bisboronate derivatives 8a–d have PPh3 recently been reported by insertion of diazoalkanes into R l Ph PPhPt P bis(pinacolato)diborane(4) by Abu Ali et al.37 (Scheme 3) and R2 3 3 BB O C the proposed catalytic cycle is shown in Fig. 1. A view of 8d B B O PPh3 O is shown in Fig. 2. O PPh Preparation of 1,4-dibora-2,5-cyclohexadienes (10a–c)have 3 8 been demonstrated by Wrackmeyer and Kehr.38 Organobo- BBPt ration of tetrakis(alkynyl)stannanes leads to the spiro-cyclic PPh3 compound 9 in high yield. The reactions of 9 with MeBBr2, 6 − i-PrBBr2,andPhBCl2 in dichloromethane between 78 and Rl + ◦ 25 CgiveB–C C–B (10a–c) compounds. Interconversion BBCPt Rl N R R2 2 2 7 O I CH2 B Figure 1. The proposed catalytic cycle for formation of O O O B–C–B compounds. B 2 B CH2 M = Na, K, Mg O O 1 + of these compounds gives compounds with B–C–B structures HCl O O reflux 11–13 (Scheme 4). B CH CH B 39 2 2 HO OH B–C–B compounds 15 and 16 could be synthesized O O 40 3 B CH2 B from compound 14,and18 from compound 17 (Scheme 5). HO OH Formation of a 2,5-diborabicyclo[2.1.1]-hexane 20 and its HCl 4 reflux conversion product tetracarbahexaborane (19), which also HO OH have a B–C–B structure, have been reported by Enders et al.40 B CH2 CH2 B Synthesis of carbaboron compounds has also been reviewed OH 41 HO 5 recently. The 1,1-spirobistannoles (22a–d) are an intermediate for Scheme 2. synthesis of borolenes (23); and compounds 24a,b with the Copyright 2003 John Wiley & Sons, Ltd. Appl. Organometal. Chem. 2003; 17: 327–345 Main Group Metal Compounds Recent developments in bisdiborane chemistry 329 = NiPr2 B NiPr2 -2 B + 2 Li BNiPr2 B B NiPr2 NiPr2 14 15 16 R R B Cl B SiMe2 Me3Si Cl B R B R 17 18 17a. R = tBu 17b. R = 2,4,6-trimethylphenyl Cl Figure 2. The proposed view of the geminal organoboron B −LiCl B compound 8d, showing the atom-numbering scheme. + 2 Li B B Cl iPr Me Me iPr + Sn( )4 2 B(i-Pr)3 iPr BSnBiPr iPr iPr Me Me H 9 B Me iPr B B > 20 °C 10a. R = Me B RBX2 10b. R = iPr R B B iPr H H H 10c. R = Ph + Me iPr Me iPr 10 X H Sn B iPr X 19 20 Me iPr Scheme 5. = R R X Cl, Br B B iPr iPr Me B–C–B structure were prepared from the reaction of tetra-1- Me alkynyltin (21) with triethylborane (Scheme 6).42 Another B–C–B compound, 2,5-diborylated 3-borolene Me iPr Me iPr B B (26) could be obtained by reacting 25 and MeBBr2 in a 1 : 2 R R ratio (Scheme 7).42 11 12 The synthesis of heterodiborolanes 27 and 28 withaB–C–B structure has been demonstrated in the papers by Siebert and R R coworkers (Scheme 8).43,44 iPr B iPr B Me Me iPr Me iPr GEMINAL ORGANOBORON COMPOUNDS B B R R The chemistry of geminated boron compounds has been 13 reviewed recently.22,23 The synthesis of (diethylcyclo- propyl)borane or cyclopropyl-9-BBN was performed by dihy- Scheme 4.
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