Ring compounds hydrides

Synthetically useful stereoselective reductions have been possible with cyclic carbonyl compounds of rigid conformation. Reduction of substituted cyclohexanone and cyclopentan-one rings by hydrides of moderate activity, e.g. NaBH (J.-L. Luche, 1978), leads to alcohols via hydride addition to the less hindered side of the carbonyl group. Hydrides with bulky substituents 3IQ especially useful for such regio- and stereoselective reductions, e.g. lithium hydrotri-t-butoxyaluminate (C.H. Kuo, 1968) and lithium or potassium tri-sec-butylhydro-borates or hydrotri-sec-isoamylborates (=L-, K-, LS- and KS-Selectrides ) (H.C. Brown, 1972 B C.A. Brown, 1973 S. Krishnamurthy, 1976). 

According to Baeyer, the first member of the series of strained carbon hydride ring compounds is ethylene (n=2). Our last basic statement connects ring strain with ir-bond strength. 

Trimethylsilyl-protected 1-isopropenylcyclobutanols were rearranged to cyclohexanones via a two-step reaction sequence.114 The vinylcyclobutanes 1 were first treated with mercury(II) trifluoroacetate. The crude products were then converted into chlorides (which can be isolated) and finally reduced with tributyltin hydride to give 2. Sometimes small amounts of five-mem-bered ring compounds, which are intermediates of this two-step ring enlargement, are formed as side products. 

The predominant property of these salts is the ease with which nucleophiles add to the quinolinium-2-and the isoquinolinium-1-positions. Such additions are favoured in these bicyclic compounds since the products retain a complete aromatic benzene ring. Hydroxide, hydride and organometaUic nucleophiles aU add with facility, though the resulting dihydroaromatic products require careful handling if they are not to disproportionate or be oxidised. " This approach can give 2-nifluoromethyl-quinolines CFj carbanion (from trifluoro(trimethylsilyl)methane and fluoride) is added to an A -(para-methoxybenzyl)-quinolinium salt, then the A -substituent is removed and oxidation to the aromatic level achieved with ceric ammonium nitrate. ... 

Pentadiene and dialkyl alanes give addition products from which only pentane is split off on hydrolysis (88). Nothing further is known yet about the constitution of these compounds, e.g., if aluminum heterocycles (6- or 5-ring compounds) are formed. Tris(3,3-dimethyl-pentamethylene) dialane is said to be formed from 3,3-dimethyl-l,4-pentadiene and di-isobutylaluminum hydride in 98% yield, even under forcing conditions at elevated temperatures (160°C). The compound distills at low pressures (b.p.io-t 132°-140°C) (212). 

Fortschritte der Chemischen Forschung, F. Boscke, ed., New Results in Boron Chemistry, Springer Verlag, 1970 (borates, B—N ring compounds, lower hydrides). 

Photochemical coupling of the hydride of the six-membered ring, using t-butoxy radical as a hydrogen-abstracting reagent, produces a bi-ring compound ... 

The diacetoxymonomethoxy vinyl ether derivative shown has been used in a radical cyclisation procedure with tributyltin hydride to furnish a mixture of cyclic ethers in 87% yield of which 70% comprises a five-membered ring compound. Hydrolysis and oxidation of this with dichlordicyanobenzoquinone resulted in... 

The 5-keto acid 11 is supposed to be formed by hydroboration and oxidation of the terminal CC double bond in 12, feasible by allylation of the enone 13. Enone 13, once again, originates from an intramolecular Knoevenagel alkenylation of the a,5-diketone 14 prepared by addition of ethylmagnesium halide to the enol lactone 15 of the 5-keto acid 16. Preceding this keto acid, the allyl compound 17 is formed by nucleophilic opening of the cyclopropane ring with hydride and mefliylation in a position of the carbonyl in the cyclopropyl ketone 18. 

It may prove possible to isolate some halogen derivatives of the numerous polyphosphorus hydrides which are now known (Chapter 2.5). The hexameric ring compounds (PCl)g (4.286a) and (PBr)g have been prepared by reaction (4.287), but these compounds appear to be stable only in dilute solutions at low temperatures [37]. 

Radical Reactions. The a-p-tolylsulfonylmethyl radical, generated using either tributyltin hydride, azobisisobutyro-nitrile, or hexabutyldistannane with UV irradiation, adds to enol ethers, enatnines, and silyl enol ethers. The addition to enam-mes shows considerable syn diastereoselectivity which can be explained on the basis of an allylic 1,3-strain model (eq 11). When an alkenic or alkynic moiety is present in the a-substituent of the a-p-tolylsulfonylmethyl radical, cyclization can occur to give five-membered ring compounds (eqs 12 and IS). ... 

Medium ring compounds commonly show enhanced solvolysis rates and solvolysis products derived from transannular hydride transfer. Ionisation in these systems may take place with some degree of transannular C—H bond participation, the extent of bridging in the transition state and competitive nucleophilic solvent assistance (A s-process) being broadly and independently variable. 

Transient Three-membered-Ring Compounds.—A review on protonated cyclopropanes as reactive intermediates has appeared. The reaction of methylcyclo-propane with proton is predicted, by EH-MO calculations, to involve two dominant paths (i) removal of hydride ion to generate cyclopropylcarbinyl cation, and (ii)... 

A ring compound with a repeating BCN sequence (XXIa) is obtained in low yield from sodium hydride and H2B[N(CH3)3] C1 183a). 

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