Silane, triethyl

Ojima has reported a rhodium-catalyzed protocol for the disilylative cyclization of diynes with hydrosilanes to form alkylidene cyclopentanes and/or cyclopentenes. As an example, reaction of dipropargylhexylamine with triethyl-silane catalyzed by Rh(acac)(GO)2 under an atmosphere of CO at 65 °G for 10 h gave an 83 17 mixture of the disilylated alkylidene pyrrolidine derivative 92b (X = N-//-hexyl) and the disilylated dihydro-1/ -pyrrole 92c (X = N-//-hexyl) in 76% combined yield (Equation (60)). Compounds 92b and 92c were presumably formed via hydrosilyla-tion and hydrosilylation/isomerization, respectively, of the initially formed silylated dialkylidene cyclopentane 92a (Equation (60)). The 92b 92c ratio was substrate dependent. Rhodium-catalyzed disilylative cyclization of dipro-pargyl ether formed the disilylated alkylidene tetrahydrofuran 92b (X = O) as the exclusive product in low yield, whereas the reaction of dimethyl dipropargylmalonate formed cyclopentene 92c [X = C(C02Et)2] as the exclusive product in 74% isolated yield (Equation (60)). 

This product is then treated with acryloyl chloride. The initial step in this case probably involves the acylation of nitrogen on the enamine conjugate addition then completes the formation of the lactam ring (23-5). Treatment of that product with triethyl silane then reduces the ring unsaturation and cleaves the benzylic nitrogen bond on the auxiliary to yield (23-6) as the optically pure tmns isomer. Displacement of bromine with the mercapto benzthiazole (23-7) completes the synthesis of izonsteride (23-8) [25]. 

The popular approach to tetrahydrofurans involves an electrophilic process and the commonly used electrophiles for the cyclization are acids, oxygen, halogen, mercury (see Section 3.11.2.2.9) and selenium. The ionic hydrogenation of furans with excess triethyl-silane in trifluoroacetic acid affords high yields, e.g. 2-methylfuran is reduced to 2-methyl-tetrahydrofuran and 2-ethylfuran to 2-ethyltetrahydrofuran (see Section 3.11.2.5). The synthesis of several dihydro and tetrahydrofurans containing natural products by chirality transfer from carbohydrates has been used successfully for total synthesis, e.g. (-)-nonactic acid. A reasonable yield of 2-alkyltetrahydrofuran was prepared from 4-alkylbut-l-en-4-ol by hydroboration followed by cyclization with p-toluenesulfonic acid. 

Vinyl-2-norbornene triallylcyanurate Vinyl triethyl silane... 

Diphenyl-(1-phenyl-propyl)- E2, 147 Diphenyl-(2-phcnyl-vinyl)- E2, 66 Diphenyl-[2-(/ranv-2-phcnyl-vinyl)-phenyl)-aus Diphenyl-(2-phenyl-ethinyl)-phosphan und wasserhaltigem Ethanol E2, 48 Diphenyl-(phthalimino-methyl)- E2, 22 Diphenyl-piperidinomethyl- XII/1, 155 Diphenyl-1-propinyl- E2, 76 Diphenyl-tosyloxymethyl- El, 513 Diphenyl-(3-trialkylsik>xy-a]]yD- E2, 27 Diphenyl-trichlormethyl- XII/1, 151 F.2, 23 (Z)-Diphenyl-(3-triethylsilyloxy-allyl)- E2, 27 (Z)-Diphenyl-(3-triethylsilyloxy-2-butenyl)-aus Diphenyl-methoxy-phosphan und Chlor-triethyl-silan/3-Oxo-l-butcn E2, 27 Diphenyl-trifluoracctyl- E2, 8, 19, 42 Diphenyl-(2,2,2-lrifluor-ethyl)- E2, 16 Diphenyl-(l,l,3-trimethyl-2-butenyl)- E2, 71 Diphenyl-(trimethylsilyl-methyl)- E2, 22, 66 Diphcnyl-(l-trimethylsilyloxy-alkyl)- E2, 26 Diphenyl-triphenylmethyl-XlI/1,151 Diphenyl-(triphenylstannyl-methyl)-... 

Figure 13 Ultrafast kinetics of /j5-CpMn(CO)3 in neat room-temperature triethyl-silane after (a) 295 mn and (b) 325 nm photolysis. In each panel, the transients are normalized against that of the singlet / 5-CpMn(C.O)2(Et3SiH) to demonstrate a reduced singlet-to-triplet ratio when excited at a longer (325 nm) wavelength. The time constants for the exponential fits are also shown in the plots. (Adapted from Refs. 45 and 46.)...

A reductive removal of a propargylic hydroxy group using triethyl silane followed by a reductive decomplexation... 

The reaction of conjugated enones and dienones with trimethyl- and triethyl-silane in the presence of TiCU, followed by aqueous work-up produces the corresponding saturated ketones. This Lewis acid catalysis is particularly useful for conjugated reduction of sterically hindered systems (Scheme 46). " a,p-Unsaturated esters are not reduced under these conditions. 

However, we know of no report of the reduction of a ketone to a methylene compound using boron trifluoride etherate and triethyl silane. 

Ionic Hydrogenation with Triethyl Silane and Boron Trifluoride... 

Tributyltin hydride has been used as a hydride donor to produce stabilized car-benium ions in 2-oxonia Cope rearrangement use of the less nucleophilic triethyl-silane resulted in poor chemical and optical yields (Scheme 12.129) [232]. 

HYDROGENATION CATALYSTS Chloro-platinic acid-Triethyl silane. Lindlar catalyst. Nickel boride. Osmium-on-carbon. Palladium hydroxide. Tris(triphenylphos-phine)chlororhodium. 

A McMurry coupling of (176, X = O Y = /3H) provides ( )-9,ll-dehydroesterone methyl ether [1670-49-1] (177) in 56% yield. 9,11-Dehydroestrone methyl ether (177) can be converted to estrone methyl ether by stereoselective reduction of the C9—C11 double bond with triethyl silane in trifluoroacetic acid. In turn, estrone methyl ether can be converted to estradiol methyl ether by sodium borohydride reduction of the C17 ketone (199,200). 

A convenient preparation method involves PdCL-catalyzed reaction of triethyl-silane and Mel at room temperature. Other silyl iodides are obtainable in the same manner (6 examples, 77-97% yield). 

Although outside the specific realm of oxindole synthesis, an interesting intramolecular route into a spiroindoline scaffold has been reported by Amat, Bosch, and coworkers who unexpectedly observed the Lewis-acid catalyzed cyclization of tryptophan derived oxazolopiperidone lactams 120 in the presence of triethyl silane [73]. In the event, spiroindoline 122 was obtained as a single stereoisomer in 86% optimized yield (Scheme 32). It was demonstrated that the hydroxymethyl group of the ring-opened oxazolidine was important for directing the stereochemical outcome of the transformation as removal of the ethyl side chain of the lactam ring did not diminish the selectivity of the spirocyclization. 

Toward this end, the henzylamine 239 was treated with 2-(phenylthio) acetyl chloride (240) in hot toluene acylation of the alkyl amine resulted in an isogramine type fragmentation to furnish dihydrocarbazole 241. Reduction using triethyl silane, followed by oxidation of the thioether sulfur employing mCPBA, led to srrlfbxide 242. 

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