Chelat‐stabilisierte 1,3‐Bis(acyloxy)‐1,3‐diethyldiboroxane aus Triethylboroxin und Carbonsäureanhydriden

Abstract

Chelate-Stabilized 1,3-Bis(acyloxy)-1,3-diethyldiboroxanes from Triethylboroxin and Carboxylic Acid Anhydrides['"]Triethylboroxin (A) reacts with carboxylic acid anhydrides (RC0)20 [R = Me: la; Et: lb; tBu: Id; Ph: l e ] with various rates to give high yields of the 3,7-dialkyl-lV5-diethyl-4,8,9trioxa-2,6-dioxonia-1,5-diboratabicyclo[ 3.3.l]nona-2,6-dienes dB(Et)OC(R)Ok(Et)OC(R)O (2) [R = Me: 2a (X-ray crystal structure analysis); Et: 2b; tBu: 2d; Ph: 2e], presumably via the unstable compounds bB(Et)OB(Et)OC(R)Ok(Et)OC(R)O (3a, b, d, e). Compound l c (R = CF3) reacts with A to form a mixture of 1,3-diethyl-1,3-bis(trifluoroacetoxy)diboroxane O=C(CF,)OB(Et)OB(Et)O(CF3)C=0 (2c') and 2c (R = CF,) at room temperature. Whereas two compounds of the type 2 do not comproportionate, l a -e spontaneously form the mixed substituted carboxylic acid anhydrides l a b etc. on mixing at room temperature (GC, I3C NMR). -From the I r 0enriched A* and l a -e the '?O-enriched compounds 2a*-e* with BO*B and > BO*OCR groups are obtained. A* exchanges 0 atoms up to 200°C with succinic anhydride (If) forming If* or with phthalic acid anhydride ( l g ) forming l g ' and 3g*. -The mixed carboxylic acid anhydrides lxy are cleaved, and the mixtures of 1 are separated with A to yield the uniform 3,7-dialkyl-substituted compounds 2.In unsere Untersuchungen zur Ubertragung von Sauerstoffatomen auf und von Organobor-Verbindungen[*I haben wir das praparativ vielseitig venvendbare Triethylboroxin einbezogen und berichten hier uber dessen Reaktionen rnit den Carbonsaureanhydriden (RCO)20 (la-e). Auf einem einfachen, ubersichtlichen Weg konnten dabei die zweifach ringstabilisierten 1,3-Bis(acyloxy)-1,3-diethyIdiboroxane 2a-e hergestellt und daruber hinaus die Komproportionierung der Anhydride 1 a-e zu den gemischt-substituierten Verbindungen lab-lae analytisch nachgewiesen werden.Zum Verfolgen der Reaktion nach G1. (a) haben wir 1 7 0angereichertes Triethylboroxin eingesetzt und dessen Verhalten auch gegenuber den cyclischen Anhydriden If und l g untersucht. Diethylborylpivalat (B)I41 und Tetraethyldiboroxan (C)I51 sind zusatzlich fur regioselektive I7O-Dotierungen verwendet worden. Herstellung von 2a-e aus A und la-eDie praparative Gewinnung der gemischten Anhydride 2a-e aus Triethylboroxin (A) und den Carbonsaureanhydriden la-e nach der G1. (a) liefert keine Nebenprodukte, im Gegensatz zu allen bisher durchgefuhrten ReaktionenI6].1,3-Bis(acyloxy)-l,3-diorganodiboroxane, die in Losung bevorzugt und im festen Zustand ausschliefilich als Chelatstabilisierte 4,8,9-Trioxa-2,6-dioxonia-l,5-diboratabicyclo-[3.3.1]nona-2,6-diene (2) v~rliegen[~.~I, sind meist unter Verwendung protonenhaltiger Verbindungen hergestellt worbeispielsweise aus Triorganoboranen, (Acy1oxy)dialkylboranen oder Tetraorganodiboroxanen mit freien Carbonsauren[8a] sowie aus Alkyldihydroxyboranen[8b] mit Carbonsaureanhydriden. Auch Halogen-organoborane wurden mit Carbonsauren in die Diboroxane des Typs 2 ubergefiihrt[8cl. Triethylboroxin (A), das sich u.a. zur Herstellung von Triethyl...

Mechanistic insights into boron-catalysed direct amidation reactions

“…6 ) which is structurally related to analogous complexes reported elsewhere. 22 Interestingly, in a separate NMR reaction, addition of an excess of phenylacetic acid to boronic acid 8c , in the presence of 5 Å MS shifted the equilibrium even further towards the “ate”-complex as seen by 11 B NMR (see further examples in the ESI † ).…”

Indirect Nuclear Spin-Spin Coupling Constants 1J(17O,11B). First Observation And Calculation Using Density Functional Theory (Dft)

“…for the borane adducts 14a, b; the FC term becomes small in the case of the borate 13 and changes its sign in the borates 3a, b. The situation for the FC contribution to the coupling constants 1 J( 17 O, 13 C) for all sp 3 -hybridized carbon atoms [36b] is similar to that for 1 J( 17 O, 11 B) in the borane adducts 14a, b. The PSO contribution can be of either sign, and cannot be neglected as is evident in the case of 13.…”

“…In addition to routinely applied 1 H and 13 C NMR spectroscopy, many boronoxygen compounds have been studied extensively by 11 B NMR [1,2], allowing to distinguish readily between three-and four-coordinate boron atoms, and revealing information on equilibria and also on the nature of other substituents at the boron atom. Few studies have been carried out on boron-oxygen compounds focusing on 17 O NMR at natural abundance in solution [3 -5], and it has been shown that the chemical shifts δ 17 O cover a rather large range (ca.…”

Synthesis and characterization of novel intramolecularly base-stabilized BEt2 and BEt derivatives: molecular structures of 1-Et2BOCPh2-2-NMe2C6H4, 1-(CH3COO)EtBOCCy2-2-NMe2C6H4 and BEt(1-OCPh2CH2-2-NMe2C6H4)2

“…2:1) (7). This demonstrates the presence of two types of boron compounds, presumably with tricoordinate (sp 2 ) and tetracoordinate (sp 3 ) environments [11]. The chemical shifts of around 32 ppm are indicative of a tricoordinate (sp 2 ) boron atom, although this value is shifted to high field compared with those reported in the literature [12]; on the other hand, the signals at ca.…”