Ketones propargyl

Tributylallenyltin reacts smoothly with acetyl chloride in the presence of a small amount of zinc chloride to give methyl propargyl ketone in a reasonable yield ... 

General note. The propargyl ketone is extremely base-sensitive. Traces of alkali... 

Figure 7.25 Enzymatic reduction of a-halogenated propargylic ketones by LBADH...

Ketones and aldehydes possess the highest a-acidity, many examples being known. In fact, it is usually very difficult to keep a terminal propargyl ketone from isomerizing to the allenyl ketone. Thus the oxidation of a homopropargylic alcohol 54, a typical precursor, in most of these cases directly delivers the allenyl ketones 56 rather than the propargyl ketones 55 in high yields [92-109] (Scheme 1.23). 

Scheme 2.2.7.19 Chiral building blocks evolved from enantioselective enzymatic reduction of propargylic ketones D.

In research on ketones as nucleophiles, Hashmi et al. studied the cycloisomerization of propargyl ketones. Reaction took place by nucleophilic attack of the ketone followed by aromatization to furan [28] (Scheme 8.25). 

For the synthesis of furanones, Kirsch et al. studied the gold-catalyzed hetero-cyclization/1,2-migration cascade reaction of a-hydroxy propargyl ketones [139]. 

The reaction of 1 with propargylic ketones shows only moderate enantioselectivity (35-50% ee). 

Chiral propargylic alcohols. The ketals (2) obtained from propargylic ketones and (2R, 4R)-2,4-pentanediol (1) are cleaved by DIBAH or Br2AlH to the ethers (3) diastereoselectively ( 96 4). The chiral auxiliary is removed by oxidation (PCC) and hydrolysis to furnish optically pure propargylic alcohols with the (R)-configuration.1... 

In a more recent publication Hashmi et al. reported that propargyl ketones such as 20 and allenyl ketones such as 21 can be cyclized to furans such as 22 in reactions catalyzed by gold(III) chloride (Scheme 5) [12]. This type of reaction had already been described as a... 

Acetylenic ketones are important synthetic intermediates in the synthesis of a variety of natural products. Optically active propargyl alcohols of either configuration are readily available in high optical purity by asymmetric reduction of propargyl ketones with B-3-pinanyl-9-borabicyclo(3.3.1)nonane761 (Eq. 31). 

The conversion of a diol or bromohydrin to the corresponding epoxide is a well-known and useful method. Recently two methods have been reported that significantly add to this chemistry. A synthesis of a key component of the natural product neocarzinostatin has been reported <07OL45>. In this work, an allenyl zinc bromide was added to a propargylic ketone to provide a chlorohydrin stereoselectively. Treatment of the chlorohydrin with base provided the epoxide. 

Stereoselective reduction of a chiral a-methylpropargyl ketone. (R)-l, prepared from (-l-)-a-pinene, reduces the steroidal propargyl ketone 2 to 3 and 4 with higher than expected diastereoselectivity (24 1). In contrast, (S)-l reduces 2 slowly and incompletely, with low cnantioselectivity. 

The double conjugate addition of dithiols to propargylic ketones offers a facile route to [3-keto 1,3-dithianes that can function as masked 1,3-dicarbonyl compounds and provide access to spiroketals. When the alkynic substrate contains an additional electrophilic centre, a tandem eyclisation can accompany thiane formation (Scheme 30) <03OBC15>. 

The highly reactive carbonyl of lactone (60), an intermediate in the synthesis of forskolin, was easily converted to propargyl ketone (61) by addition of the lithium alkynide as shown in equation (48). It is possible that the intermediate ketal alkoxide was not stable in solution because of ring strain however, no multiple addition products were reported, nor was there any Michael addition of the alkoxide to the resulting ynone. 

The first total synthesis of the neuritogenic spongean polyacetylene lembehyne A was accomplished by M. Kobayashi and co-workers. The single stereocenter of the molecule was introduced via the Midland reduction of a propargylic ketone using an Alpine-Borane , which was prepared from (+)-a-pinene and 9-BBN. 

Midland, M. M., Tramontane, A., Kazubski, A., Graham, R. S., Tsai, D. J. S., Cardin, D. B. Asymmetric reductions of propargyl ketones. An effective approach to the synthesis of optically active compounds. Tetrahedron 1984,40, 1371-1380. 

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