Synthesis of 4‐silaspiro[3.4]octa‐1,5‐diene derivatives: hybrid spiro compounds

Abstract

Trialkynyl(vinyl)silanes CH 2 ¼CH-Si(CC-R) 3 (R = Bu, Ph, p-tolyl) were prepared and treated with 9-borabicyclo[3.3.1]nonane (9-BBN). Consecutive 1,2-hydroboration and intramolecular 1,1-carboboration reactions (each requires different reaction conditions) were studied. 1,2-Hydroboration of the Si-vinyl group takes place at ambient temperature (23°C in tetrahydrofuran), followed by intramolecular 1,1-vinylboration to give 1-silacyclopent-2-ene derivatives, bearing still two alkynyl functions at the silicon atom. Further treatment with a second equivalent of 9-BBN affords 1-alkenyl-1-(alkynyl)-1-silacyclopent-2-ene derivatives. These undergo intramolecular 1,1-vinylboration to give 4-silaspiro[3.4]octa-1,5-dienes bearing the boryl groups at 2 and 6 positions. Protodeborylation of all new compounds (intermediates and final products) using acetic acid in slight excess afforded corresponding silanes including spirosilanes. All compounds were characterized using multinuclear NMR spectroscopy ( 1 H, 11 B, 13 C, 29 Si) in solution state. Solid-state structures for one of the trialkynyl(vinyl)silanes (R = p-tolyl) and one of the 1-silacyclopent-2-ene derivatives (R = Ph) were confirmed using X-ray diffraction.

Recent Advances in Boron‐Substituted 1,3‐Dienes Chemistry: Synthesis and Application

“…1,1‐Carboboration of dialkynyl‐ and tetraalkynylsilanes opens a convenient route to cyclic silanes such as siloles 60 or bisiloles 56 . The reaction with alkynyl(diorgano)tin compounds (R 1 2 Sn(C≡C‐R 2 ) 2 leads to boron‐functionalized 4‐stannabora‐cyclohexa‐2,5‐dienes although rather harsh reaction conditions (heating for a long period at 100–120 °C) are required when trialkylboranes (BR 3 ; R=Me, Et), Et‐9‐BBN, BPh 3 , and B(C 6 F 5 ) 3 are used . Organometallic‐substituted allenes obtained by 1,1‐organoboration of bis(trimethylstannyl)ethyne with trimethylsilyl‐ and dimethylsilyldialkylboryl‐substituted alkenes have been reported by Wrackmeyer .…”

1,1‐Carboboration through Activation of Silicon–Carbon and Tin–Carbon Bonds

“…Applications and the mechanism of 1,1‐carboboration of dialkynyl derivatives are demonstrated, and this is extended to Si‐ and Sn‐tetraalkynyl derivatives, and even to the Sn–C= bond in dimethyl(divinyl)stannane. Finally, the combination of the well‐known 1,2‐hydroboration15,18 and the more recent 1,1‐carboboration is introduced,3a,19–28 offering most attractive routes to new silicon heterocycles such as fused silole derivatives and spirosilanes.…”

“…The intermediates involved in this reaction survive in solution for a sufficiently long time to allow NMR spectroscopic data ( 11 B, 1 H, 13 C and 29 Si NMR) to be recorded. Even a protodeborylated 1‐silacyclopent‐2‐ene as an intermediate containing the remaining Si(C ≡C–R ) 2 unit has been isolated and characterized by multinuclear NMR spectroscopy and X‐ray diffraction 28…”

“…The reactions have been successful for nearly all the compounds (intermediates and final products) except in the case of the t Bu‐substituted 5‐silaspiro[4.4]nona‐1,6‐diene derivative 20,25. Some representative examples are given in Scheme (for more details see22,27,28).…”

An Unusual and Facile Synthetic Route to Alumoles

“…As a consequence, we isolated intermediate 9 (colorless crystals, yield of 67 %, Scheme 3). Unexpectedly compound 9 is remarkably stable, and its further conversion [8]: Al(1)-N(1) 1.9460- (15), Al(1)-N(2) 1.8626 (15), Al(1)-C(1) 1.9886 (18), Al(1)-C(4) 1.9872- (18), C(1)-C(2) 1.367(2), C(2)-C(3) 1.524(2), C(3)-C(4) 1.357(3), B(1)-C(2) 1.552(3); N(1)-Al(1)-N(2) 95.53 (6), C(1)-Al(1)-C(4) 90.60 (7). The CCDC numbers for all the structures reported herein can be found in the Supporting Information.…”