Yuri N. Bubnov

1‐Boraadamantane: Reactivity Towards Di(1‐alkynyl)silicon and ‐tin Compounds: First Access to 7‐Metalla‐2,5‐diboranorbornane Derivatives

1-Boraadamantane (1) reacts with di(1-alkynyl)silicon and -tin compounds 2 (Me2M(C...CR)2: M=Si; R=Me (a), tBu (b), SiMe3 (c); M=Sn, R=SiMe3 (e)) in a 1:1 ratio by intermolecular 1,1-alkylboration, followed by intramolecular 1,1-vinylboration, to give siloles 5a-c and the stannole 5e, respectively, in which the tricyclic 1-boraadamantane system is enlarged by two carbon atoms. Owing to the high reactivity of 1, a second fast intermolecular 1,1-alkylboration competes with the intramolecular 1,1-vinylboration as the second major step in the reaction if the substituent R at the C...C bond is small (2a) and/or if the M-C... bond is also highly reactive, as in 2d (M=Sn, R= Me) and 2e (M=Sn, R=SiMe3). This leads finally to the novel octacyclic 7-metalla-2,5-diboranorbornane derivatives 8a, 8d, and 8e, of which 8e was characterized by X-ray analysis in the solid state. 1,1,2,2-Tetramethyldi(1-propynyl)disilane, MeC...C-SiMe2SiMe2-C...CMe (3), reacts with 1 to give mainly a 1,2-dihydro-1,2,5-disilaborepine derivative 9 and the octacyclic compound 11, which is analogous to 8a but with an Me4Si2 bridge. All new products were characterized in solution by 1H, 11B, 13C, 29Si, and 119Sn NMR spectroscopy. For 8 and 11, highly resolved 29Si and 119Sn NMR spectra revealed the first two-bond isotope-induced chemical shifts, 2delta10/11B(29Si) and 2delta10/11B(119Sn) respectively, to be reported.

Reactivity of some poly-1-alkynylsilicon and -tin compounds towards triallylborane—routes to novel heterocycles

Abstract Triallylborane reacts with most poly-1-alkynylsilanes ( 1 – 5 ), containing up to four CC units, or di(1-alkynyl)tin compounds ( 6 ) to give either siloles ( 8 , 11 , 14 , 16 ), as the result of an intermolecular 1,1-allylboration followed by an intramolecular 1,1-vinylboration, or the novel 2-alkylidene-1,3-silaborolene ( 9 ) or 2-alkylidene1,3-stannaborolene derivatives ( 17 ), as the result of intermolecular 1,1-allylboration followed by an intramolecular 1,2-allylboration. In the case of the borolene derivatives, a second intramolecular 1,2-allylboration takes place to give 1,7-borasila- or 1,7-borastannabicyclo[4.3.0]nona-5,8-diene derivatives ( 10 , 12 , 13 , 15 , 18 ). If the starting materials are di(1-alkynyl)methylsilicon hydrides ( 2 ), the latter reaction affords selectively only one diastereomer ( 10 ( H )). All products were characterised by extensive multinuclear magnetic resonance spectra ( 1 H-, 11 B-, 13 C-, 29 Si-, and 119 Sn-NMR).

1-Boraadamantane: reactivity towards mono-1-alkynyltin, -germanium and -silicon compounds — synthesis of 4-methylene-3-borahomoadamantanes

The reaction of 1-boraadamantane 1 with 1-alkynyltin (3), -germanium (4), and -silicon compounds (5) leads to enlargement of the tricyclic system by formation of 4-methylene-3-borahomoadamantanes (6–9). These are 1,1-organoboration reactions which proceed by cleavage of the MC bond (M=Sn, Ge, Si). There is evidence for 1,1-deorganoboration which apparently take place much more readily than for non-cyclic analogues, most likely as the result of the strained tricyclic system. When 2-ethyl-1-boraadamantane (2) is used, again 3-borahomoadamantanes are formed, the isomers 15–18. The product distribution is sensitive to steric effects. However, it appears that the BC(H)Et bond in 2 is slightly more reactive than the BCH2 bonds. All products were characterised by 1H-, 11B-, 13C-, 29Si- and 119Sn-NMR.

Preparation of trans-2-allyl-6-alkyl(aryl)-1,2,3,6-tetrahydropyridines by reductive trans-2,6-dialkylation of pyridine. Synthesis of (±)-epidihydropinidine

Abstract A convenient method for the preparation of the title compounds involving the sequential treatment of pyridine with RLi ( R = Alk , Ar ), triallylborane and methanol is developed.

Reactivity of mono-1-alkynyltin and -germanium compounds towards triallylborane

Abstract Triallylborane, All3B (4), reacts with trialkyl(1-alkynyl)tin compounds 1 R3SnCCR1 [R=Me, R1=Me (a), tBu (b), Ph (c), SiMe3 (d), SnMe3 (e)] and 2 (R=Bu, R1=ferrocenyl) and also with 1-phenylethynyl(trimethyl)germanium (3c) preferably by 1,1-allylboration to give the organometallic-substituted alkenes 6, 8 and 10. In the cases of 1b and 1d, allyl/alkynyl exchange takes place instead. However, the formation of the alkene 6e was observed at −30°C. In the case of 1c, 1,2-allylboration, leading to the alkene 7c, competes with 1,1-allylboration, the ratio 6c/7c being dependent on the polarity of the respective solvent (more of 6c in a more polar solvent). All3B proved to be much more reactive than triethylborane, Et3B (5). All products were characterised by 1H, 11B, 13C and 119Sn NMR.

Reactivity of 1,6-bis(trimethylsilyl)-hexa-3-ene-1,5-diynes towards triethylborane, triallylborane, and 1-boraadamantane: first molecular structure of a 4-methylene-3-borahomoadamantane derivative, and the first 6,8-diborabicyclo[2.2.2]oct-2-ene derivative.

Compounds (E)- (1) and (Z)-1,6-bis(trimethylsilyl)-hexa-3-ene-1,5-diyne (2) react with triethylborane (3) by 1,1-ethylboration in a 1:1 or 1:2 molar ratio (in the case of 1), whereas in the case of 2 only the 1:1 product is formed. The analogous reactions of 1 or 2 with triallylborane (4) are more complex because of competition between 1,1-allyl- and 1,2-allylboration. Again, compound 2 reacts only with one equivalent of 4. In the case of 1-boraadamantane (5), 1,1-organoboration of 1 and 2 takes place either at one or at both C[triple bond]C bonds leading to compounds containing the 4-methylene-3-borahomoadamantane unit(s). The product of the reaction of 1 with two equivalents of 5 was characterized by X-ray structure analysis. The primary products of the reaction of 2 with 5 rearrange upon heating by deorganoboration and organoboration to give finally a tetracyclic compound 24 that contains an exocyclic allenylidene group. The product of the 1:2 reaction of 2 with 5 rearranges to give the 6,8-dibora-bicyclo[2.2.2]oct-2-ene derivative 25. All reactions were monitored by (1)H, (11)B, (13)C, and (29)Si NMR spectroscopy.

Die erste Si‐H‐B‐Brücke: Kombination von 1,1‐Organoborierung und Hydrosilylierung

Eindeutig aktiviert ist die Si-H-Bindung von 1, das durch Umsetzen von Triallylboran mit Bis(dimethylsilyl)ethin erhaltlich ist, wegen der Nachbarschaft eines dreifach koordinierten Boratoms [Gl. (1)]. So reagiert 1 ohne Katalysator (!) in einer intramolekularen Hydrosilylierung zu 2.

trans-cis-Isomerization of trans-2-allyl-6-alkyl(aryl)-1,2,3,6-tetrahydropyridines on heating with triallylborane. Synthesis of (±)-dihydropinidine

Abstract A convenient method for isomerization of trans-2-allyl-6-alkyl(aryl)-1,2,3,6-tetrahydropyridines into the corresponding cis-isomers is presented.

2-dipropylborylmethyl-1,3-butadiene - a new reagent for isoprenylation. Efficient synthesis of ipsenol and ipsdienol

Abstract A simple and convenient method for isoprenylation of carbonyl compounds and ethoxyacetylene using the titled new boron containing “isoprene C-5 synthon” and application of this efficient procedure to the synthesis of ipsenol and ipsdienol are described.

From bis(silylamino)tin dichlorides via di(1-alkynyl)-bis(silylamino)tin to new heterocycles by 1,1-organoboration

Bis(silylamino)tin dichlorides 1 [X 2 SnCl 2 with X=N(Me 3 Si) 2 ( a ), N(9-BBN)SiMe 3 ( b ), N( t Bu)SiMe 3 ( c ), and N(SiMe 2 CH 2 ) 2 ( d )] were prepared from the reaction of two equivalents of the respective lithium amides ( Li - a – d ) with tin tetrachloride, SnCl 4 , or from the 1:1 reaction of the respective bis(amino)stannylene with SnCl 4 . The compounds 1 react with two equivalents of lithium alkynides LiCCR 1 to give the di(1-alkynyl)-bis(silylamino)tin compounds X 2 Sn(CCR 1 ) 2 , 2 (R 1 =Me), 3 (R 1 = t Bu), and 4 (R 1 =SiMe 3 ). Problems were encountered, mainly with LiCC t Bu as well as with 1b , since side reactions also led to the formation of 1-alkynyl-bis(silylamino)tin chlorides 5 – 7 and tri(1-alkynyl)(silylamino)tin compounds 8 and 9 . 1,1-Ethylboration of compounds 2 – 4 led to stannoles 10 , 11 , and in the case of propynides, also to 1,4-stannabora-2,5-cyclohexadiene derivatives 12 . The molecular structure of the stannole 11b (R 1 =SiMe 3 ) was determined by X-ray analysis. The reaction of 2a and d with triallylborane afforded novel heterocycles, the 1,3-stannabora-2-ethylidene-4-cyclopentenes 14 . These reactions proceed via intermolecular 1,1-allylboration, followed by an intramolecular 1,2-allylboration to give 14 , and a second intramolecular 1,2-allylboration leads to the bicyclic compounds 15 .