5- Hexynal

An alternative route to ( )-Y-bisabolene was demonstrated starting from the acetylene B, which was made from 5-hexyn-2-one as shown ... 

FRAGMENTATION OF a,(J-EPOXYKETONES TO ACETYLENIC ALDEHYDES AND KETONES PREPARATION OF 2,3-EPOXYCYCLOHEXANONE AND ITS FRAGMENTATION TO 5-HEXYNAL... 

B. 5-Hexynal. To a solution of 5.60 g. (0.050 mole) of 2,3-epoxycyclohexanone in 120 ml. of benzene in a 500-ml. round-bottomed flask is added 10.82 g. (0.051 mole) of trans-1 -amino-2,3 diphenylaziri-dine.2 Initially, after brief swirling at room temperature, the reaction mixture is a colorless, homogeneous solution however it rapidly turns yellow and cloudy due to separation of water. After 2 hours the benzene and water are removed as an azeotrope under reduced pressure on a rotary evaporator with the bath maintained at approximately 30°. The resulting crude mixture of diastereomeric hydrazones weighs 15.4 g. (Note 7) and is subjected directly to the fragmentation reaction (Note 8). 

The contents of the receiver and trap are combined with the aid of a few drops of dichloromethane and distilled through a 15-cm. Vigreux column under reduced pressure. After only a few drops of forerun, the main fraction is 2.87-3.17 g. (60-66%) of 5-hexynal, b.p. 61-62° (30 mm.), w20d 1.4447, df 0.875 (Notes 11-13). Cas chromatographic analysis (Note 14) shows this material to contain 3-5% of unidentified impurities with longer retention times (Note 15). 

Pract -grade diethyl phthalate (obtainable from Fluka AG) should be redistilled at 126-129° (1 mm.) before use. It is stable under the reaction conditions and does not codistil with the product 5-hexynal. 

The N-aminoaziridine version7 of the a,/3-epoxyketone->alkynone fragmentation is a possible alternative in situations where the simple tosylhydrazone version6-9 fails. The tosylhydrazone method often gives good yields at low reaction temperatures, but it tends to be unsuccessful with the epoxides of enones that are not cyclic or are not fully substituted at the /5-carbon atom. For example, it has been reported9 that 2,3-epoxycyclohexanone docs not produce 5-hexynal by the tosylhydrazone route. The A-aminoaziridine method can also be recommended for the preparation of acetylenic aldehydes as well as ketones. 

HEXEN-l-OL, 55, 57, 62 Z.-j.-y )-2-Hexiilosomc acid, bis-0-(l-methyl-ethyhdene)- ](-)-2,3 4,6-Di-O-isopro-pyhdene-2-keto-L-gulonic acid, hydrate], 55, 80 5 HEXYNAL, 55,52... 

Terminal-functionalized polymers such as macromonomers and telechelics are very important as prepolymer for construction of functional materials. Single-step functionalization of polymer terminal was achieved via lipase catalysis. Alcohols could initiate the ring-opening polymerizahon of lactones by lipase catalyst. The lipase CA-catalyzed polymerizahon of DDL in the presence of 2-hydroxyethyl methacrylate gave the methacryl-type polyester macromonomer, in which 2-hydroxyethyl methacrylate acted as initiator to introduce the methacryloyl group quanhtatively at the polymer terminal ( inihator method ).This methodology was expanded to the synthesis of oo-alkenyl- and alkynyl-type macromonomers by using 5-hexen-l-ol and 5-hexyn-l-ol as initiator, respechvely. 

The SiCaC reaction of 5-hexyn-l-al 23 gives the corresponding 2-(exo-silymethylene)-l-cyclopentanol 24 in high yield (Scheme 7.11) [20]. The reaction is accelerated by gem-disubstitution for example, the reaction of 3,3-gem-disubstituted 5-hexyn-l-al 23 (X = C(C02Et)2, C(CH20Me)2) is substantially faster and cleaner than the unsubstituted derivative (X=CH2), which is accompanied by a small amount of silylformylation product [21]. It should also be noted that the formation of l-siloxy-2-methylenecyclopentane is not observed, in sharp contrast with the nickel-catalyzed version of this reaction [20]. 

SYNTHESIS AND UTILIZATION OF INDIUM (I) IODIDE FOR IN SITU FORMATION OF ENANTIOENRICHED ALLENYLINDIUM REAGENTS AND THEIR ADDITION TO ALDEHYDES (2R,3S,4S)-1-(tert-BUTYLDIPHENYLSILYLOXY)-2,4-DIMETHYL-5-HEXYN-3-OL [5-Hexyn-3-ol, 1-[[(1,1-dimethylethyl)diphenylsilyl]oxy]-2,4-dimethyl-,... 

In an extension to this work, treatment of the template with 5-hexynal under the standard dehydrating conditions furnished the cycloadduct 301 in good yield (68). However, structural analysis of both the product and the azabicyclo[3.3.0]octane-3-carboxylic acid, derived by hydrogenation of the double bond, followed by... 

Exps. 9 and 10 are convincing illustrations of the high lrineiic acidity of the ethynyl proton. In principle, there are four reaction pathways if l-bromo-5-hexyne and a strongly basic reagent are allowed to interact abstraction of the acetylenic proton, Br-metal exchange, displacement of Br by the "nucleophilic" part of the base, and elimination of HBr with formation of HCsC(CH2)2CH=CH2- Only the first process takes place under the conditions of this experiment. The kinetic stability of the intermediate LiOC(CH2)4Br is sufficient to allow for successful functionalizations with a number of reagents. For alkylations with most of the alkyl halides, the polarity of the medium will usually be insufficient. 

A mixture of 0.10 mol of l-bromo-5-hexyne (Chap. XII, exp. 1.5) and 70 ml of THF is cooled to between -60 and -80 C. A solution of 0.105 mol (slight excess) of BuLi in hexane is added drop wise over -15 min, while maintaining the temperature range indicated. Two minutes after this addition, derivatization reactions can be carried out with the clear solution. 

In the procedure for 5-hexyn-3-ol, the ammonia is replaced by DMSO before the epoxide is added. An advantage of this is that the reaction temperature can be considerably higher than... 

Although silylformylation of 3-butyn-I-ol 84 gives normal product 85 preferentially in the absence of EtsN, an appreciable amount (38%) of 7-lactone 86 is formed concomitantly." Protection of the hydroxy group in 84 leads to selective silylformylation of the acetylenic moiety as shown in Scheme 3. Hydrolysis of the silyl ether in 88 gives 85 as a single product. 4-Pentyn-I-ol 89 reacts with Mc2PhSiH under CO pressure to give a mixture of silylformylation product 90 (20%) and (5-lactone 91 (38%) after a short reaction time (0.5 h) (Equation (16)). The unusual lactone formation is not observed in the reaction of 5-hexyn-l-ol 92 in the presence of EtsN (Equation (17)). ... 

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