Tributylstannane ketones

The alkynyl ketones 840 can be prepared by the reaction of acyi chlorides with terminal alkynes, Cul in the presence of Et3N is the cocatalyst[719]. (1-Alkynyl)tributylstannanes are also used for the alkynyl ketone synthesis[720]. The a,. 3-alkynic dithio and thiono esters 842 can be prepared by the reaction of the corresponding acid chloride 841 with terminal alkynes[721,722]. 

In order to establish the correct absolute stereochemistry in cyclopentanoid 123 (Scheme 10.11), a chirality transfer strategy was employed with aldehyde 117, obtained from (S)-(-)-limonene (Scheme 10.11). A modified procedure for the conversion of (S)-(-)-limonene to cyclopentene 117 (58 % from limonene) was used [58], and aldehyde 117 was reduced with diisobutylaluminium hydride (DIBAL) (quant.) and alkylated to provide tributylstannane ether 118. This compound underwent a Still-Wittig rearrangement upon treatment with n-butyl lithium (n-BuLi) to yield 119 (75 %, two steps) [59]. The extent to which the chirality transfer was successful was deemed quantitative on the basis of conversion of alcohol 119 to its (+)-(9-methyI mande I ic acid ester and subsequent analysis of optical purity. The ozonolysis (70 %) of 119, protection of the free alcohol as the silyl ether (85 %), and reduction of the ketone with DIBAL (quant.) gave alcohol 120. Elimination of the alcohol in 120 with phosphorus oxychloride-pyridine... 

Logue MW, Teng K (1982) Palladium-catalyzed reactions of acyl chlorides with (l-alkynyl)tributylstannanes. A convenient synthesis for 1-alkynyl ketones. J Org Chem 47 2549-2553... 

The tributyltin enolates 74 are readily prepared from the corresponding enol acetates and tributyltin methoxide in the absence of solvent [34]. The tin enolates thus obtained occur in the 0-Sn form and/or the C-Sn form, and both species can be used for the aldol reaction of this system. Although the tin enolates themselves have adequate reactivity toward aldehydes [34c], in the presence of the BINAP silver(I) catalyst the reaction proceeds much faster even at -20 °C. Optimum conditions entail the use of THF as solvent and the results employing these conditions in the catalytic enan-tioselective aldol reaction of a variety of tributyltin enolates with typical aromatic, a,/3-unsaturated, and aliphatic aldehydes are summarized in Table 2. TTie characteristic features are (i) All reactions proceed to furnish the corresponding aldol adducts 75 in moderate to high yield in the presence of 10 mol % (i )-BINAP AgOTf complex at -20 °C for 8 h, and no dehydrated aldol adduct is observed (ii) with an a,j3-unsaturated aldehyde, the 1,2-addition reaction takes place exclusively (entry 3) (iii) a bulky alkyl substituent of tin enolate increases the enantioselectivity of the aldol reaction. For instance, the highest ee (95 % ee) is obtained when the tin enolate prepared from pinacolone 77 or rert-butyl ethyl ketone 79 is added to aldehydes (entries 2, 7, and 8) (iv) addition of the cyclohexanone-derived enol tributylstannane 78 (( )-... 

Alternatively, trialkylstannylcesium compounds can be prepared by fluoride ion-induced desilylation. Treatment of (trimethysilyl)tributylstannane with cesium fluoride affords a tributylstanyl anion. The anion reacts with a C-I bond to form a vinyl anion that promotes intramolecular cyclization [6]. The spiro ketone obtained is converted into a natural sesquiterpene acorone (Scheme 2.3). 

So zeigcn z. B. einfache aliphatische Ketone wie Aceton4 vom 81 bzw. T1 unterschiedliche Photoreduktions-Geschwindigkeiten gegeniiber Tributylstannan. Noch deutlicher ergibt z. B. 

Transformations. Dialkylated A -dimethyldithiocarbamoyl-acetonitriles are transformed into ketones by W-bromosuccinimide bromination or by basic hydrolysis (eq 3), and they are hydrolyzed in acidic ethanol to produce a-mercapto carboxylates. Bromination of (1) in methanol leads to the formation of l,3-dithietan-2-ylium ion. Alkylated N,N-dimethyldithiocarbamoylacetonitriles are reductively desulfurized to a-branched nitriles with tributylstannane in the presence of a catalytic amount of azobisisobutyronitrile (eq 4). ... 

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