Ketones cyclohexylidene—

Das aus (-)-Menthol hergestellte chirale Hydrid liefert in erster Linie mit zweizahnigen Substraten [fi-Amino- ketone, En-(2)-in-(4)-ole (s.S. 74)] gute optische Ausbeuten1. Als chirale vie. Diole werden Zucker-2,1 und Terpen-Derivate wie cis- und rrans-Pinandiol-(2,3)4 verwendet. Von den Zucker-Derivaten hat sich der Kom-plex mit 3-0-Benzyl-l,2-0-cyclohexyliden-a-D-glucofuranose am besten bewahrt2,5 (Vorschrift S. 74). 

Carbohydrate lactones have been used as the carbonyl reagent in the Reformatsky reaction. Thus, 2,3 5,6-di-O-cyclohexylidene-D-mannono-1,4-lactone [44, obtained by oxidation of the mannofuranose derivative (49)] reacted with ethyl bromoacetate and zinc to give the protected 2-deoxy-3-octulosonic acid ethyl ester (45a) in 69% yield (50). Ketonic hydrolysis with potassium hydroxide in aqueous methanol, followed by acidification and heating, afforded the 1-deoxyheptulose derivative 45b. Similarly, starting from compound 44, the 1-C-substituted allyl and propar-gyl lactols were prepared on reaction with allyl or propaigyl bromides in the presence of zinc (51). 

There are few reactions of aldehydes and ketones that do not in some way affect the carbonyl function. For this reason, it may be necessary to protect the carbonyl function when it is desirable to avoid reaction at this function. For example, you may plan to synthesize 4-cyclohexylidene-2-butanone by way of a Wittig reaction (Section 16-4A), which would involve the following sequence ... 

Walborsky and coworkers206 have reported the CD of series conjugated cyclohexylidene aldehydes and ketones. These compounds served as additional examples supporting the planar diene rule for CD jt tt transition208. 

The enantioselective reduction of unsymmetrical ketones to produce optically active secondary alcohols has been one of the most vibrant topics in organic synthesis.8 Perhaps Tatchell et al. were first (in 1964) to employ lithium aluminum hydride to achieve the asymmetric reduction of ketones9 (Scheme 4.IV). When pinacolone and acetophenone were treated with the chiral lithium alkoxyaluminum hydride reagent 3, generated from 1.2 equivalents of 1,2-0-cyclohexylidene-D-glucofuranose and 1 equivalent of LiAlHzt, the alcohol 4 was obtained in 5 and 14% ee, respectively. Tatchell improved the enantios-electivity in the reduction of acetophenone to 70% ee with an ethanol-modified lithium aluminum hydride-sugar complex.10... 

O-AIkylidene and -arylidene derivatives of D-gluco-, D-allo-, D-manno-, and D-talo-pyranose are difficult to prepare directly. Lem-ieux and Detert59 prepared these from the 1,2-O-ethoxyethylidene orthoester, and were able to recover quantitative yields of 1,2-O-iso-propylidene, 1,2-O-cyclohexylidene, 1,2-O-cyclopentylidene, and diastereoisomeric 1,2-O-benzylidene acetals of D-glucopyranose. In their procedure, the orthoester is allowed to react, with scrupulous exclusion of moisture, with a ketone or aldehyde in the presence of an acid catalyst. 

Stereospecific R or S Lithium aluminum hydride-3-O-benzyl-1-2-O-cyclohexylidene-a-D-glucofuranose complex. ,(3-Unsaturated ketones Li (or K) in hexamethylphosphoric triamide and ether. 

In some cases it is appropriate to use an imine instead of a carbonyl compound. Thus, benz-alaniline reacts with activated methylenes in the presence of carbocyclic acid anhydrides to give the corresponding Knoevenagel products (Scheme 21) Similarly, the enamine (170) reacts with cyanoacetic acid in ethyl acetate or dimethylformamide to afford the cyclohexylidene compound (171 Scheme 28). Acetals may be employed instead of the free ketones. An example is the reaction of fluorenone cyclic acetal (172) with malon initrile, which occurs in butanol without added catalyst to af-... 

The syntheses of carba-P-o,L-fucopyranose and carba-P D,L-galactopyranose have been reported from 3-0-benzyl-l,2 4,5-di-0-cyclohexylidene-m> o-inositol. They involved the deoxygenation of the 6-OH, the conversion of the 1-OH into a ketone, and the addition of methylmagnesium bromide (for producing the fuco derivative) or benzyloxymethyllithium (for producing the galacto derivative) followed by deoxygenation and deprotection as the key step. ... 

Lithium aluminum hydride with either 1,2-0-cyclohexylidene-D-glucofuranose or methyl 4,6-0-benzylidene-a-D-glucopyranoside (0.066 mole and 0.5 mole, respectively, with 0.5 mole LiAlH4) does constitute an asymmetric reduction system (Landor et al., 1964). Unsaturated ketones [e.g., (C.H3)2C=CHCOCH3 and CH3COC= CH] as well as dialkyl and aryl alkyl ketones have been reduced to optically active alcohols. The maximum per cent asymmetric reduction (14%) was observed with acetophenone and 1,2-0-cyclohexylidene-D-glucofuranose. 

PEEK, poly(atyl ether ether ketone) PEK, bisphenol-A polyetherketone TMBPA-PEK, tetramethylbisphenol-A PEK BPZ-PEK, PEK from cyclohexylidene TMC-PEZ, PEK from trimethyl-cyclohexylidene PEK. 

Reduction of ketones with sodium borohydride in the presence of a carboxylic acid and 1,2 5,6-di-0-cyclohexylidene-a -D-glucofuranose gave 35-50% enantiomeric enhancement values.Another group has reported a similar reaction with the corresponding di-O-isopropylidene-glucose derivative and prochiral aromatic ketones. Optical yields of up to 64% were claimed. The chiral reagents appear to be sodium acyloxyborohydrides, which complex with the carbohydrate before reduction takes place. 

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