Trialkylcarbinols

Carbon monoxide at atmospheric pressure reacts readily with trialkylboranes at 100-125° to give products that can be oxidized conveniently to trialkylcarbinols (/). 

The reaction is sensitive to the presence of water, which inhibits the migration of the third alkyl group and leads to dialkyl ketones (see Chapter 12, Section II). The convenience of the hydroboration reaction combined with the use of carbon monoxide at atmospheric pressure provides the most accessible route to many trialkylcarbinols. 

The following trialkylcarbinols (Table 12.1) may be prepared by an analogous procedure with the time required for the absorption of carbon monoxide as shown. For liquid products, the dilution with water is followed by extraction with pentane, the pentane solution is dried, and the solvent is removed (rotary evaporator), affording the pure product. 

Insertions of carbon dioxide, sulfur dioxide, and sulfur trioxide yield aluminum carboxylates, sulfinates, and sulfonates, respectively. Treatment of the resulting complexes with aqueous acid yields the corresponding aUcylcarboxylic, alkylsulphinic, and aUcylsulphonic acids. High pressure and temperatures of 220-240 °C are required for multiple insertions of CO2 to yield more than one equivalent of carboxyhc acid per aluminum. Excess aluminum trialkyl must be avoided or the initially formed carboxylate is completely alkylated to a trialkylcarbinol. Reaction of Ets A1 with CO2, for example, gives a 90% yield of triethylcarbinol. 

Trialkykarbinob. Mixed trialkylboranes, such as (I), react with carbon monoxide in the presence of ethylene glycol at 150 and 1000 psi to form 2-/-alkyl-l,3,2-dioxa-borolanes (2), which are not isolated but oxidized with hydrogen peroxide in aqueous sodium hydroxide to give trialkylcarbinols (3). Yields of isolated products arc 60-90%. 

TriaikykarUnols from trialkylhoraites. Trialkylcarbinols have been prepared by the reaction of trialkylboranes with carbon monoxide in diglyme followed by oxidation with hydrogen peroxide (equation 1). See 2. 60. The method has the disadvantage that at the temperature required isomerization of organoboranes can be significant. 

TETRALONES Methylene chloride. nilADIAZlRIDINE 1,1-DIOXIDES Sodium hydride-t-Butyl hypochlorite. THIOAMIDES Thioacetamide. TRIALKYLCARBINOLS Carbon monoxide. Lithium triethylcarboxide. TRIAZOLES Ethyl azidofomate. Sodium azide. 

THIOAMIDES Thioacetamide. TRIALKYLCARBINOLS Carbon monoxide. Lithium triethylcarboxide. TRIAZOLES Ethyl azidoformate. Sodium azide. 

Trialkylboranes give trialkylcarbinols on Hilmann carbonylation followed by oxidation . One of the most effective applications of this reaction in organic synthesis is the conversion of 1-boraadamantanes to the corresponding 1-adamantanols (Scheme 45) <76IZV2302>. 

Numerous other reactions include the synthesis of trialkylcarbinols from trialkylboranes (Brown, H. C. Acc. Chem. Res. 1969, 2, 65) and hydroboration-protonolysis leading to alkanes (Brown, H. C. Murray, K. /. Am. Chem. Soc. 1959,81,4108). Isomerization and disproportionation of the alkylboranes was also seen (reference 230b). 

Lithium triethylcarboxide Trialkylcarbinols from boranes s. 27, 892 with a,a-dichloromethyl ether instead of chlorodifluoromethane s. J. Org. Chem. 38, 2422, 3968 (1973). 

Trifluoroacetic anhydride diborane Syntheses with cyanoboranes Trialkylcarbinols from ethylene derivs. 

Preparation.—Variations continue to appear on the theme of alcohol production by hydroboration-oxidation of olefins. 5-Methoxydialkylboranes react with olefins in the presence of lithium aluminium hydride to afford a new route to trialkylboranes and thence, by carbonylation-oxidation, to trialkylcarbinols. Carbonylation with carbon monoxide is avoided in a new procedure in the presence of an excess of trifluoroacetic anhydride, trialkyl cyanoborates undergo a triple alkyl migration from boron to carbon to give, on oxidation, high yields of trialkylcarbinols (Scheme 126). Tri-... 

The first use of organoboranes for incorporating carbon isotopes was reported in 1979." In this case the carbonylation reaction was used to prepare a trialkylcarbinol, a ketone, and an aldehyde (Scheme 5.5). 

Trialkylcarbinols. A shaker tube charged with triethylborane and water, pressured with CO to 700 atm., heated gradually to 150°, and agitated 2 hrs. tris-(triethylcarbinyl)horoxine (Y 91%) stirred and treated slowly under Ng with 20% excess aq. 6 N NaOH-soln., then 20% excess aq. 30%-HgOg added dropwise, and refluxed 2 hrs. triethylcarbinol (Y 99%). F. e., also via 2,5-dihoradi-oxanes, s. M. E. D. Hillman, Am. Soc. 84, 4715 (1962). 

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