Dialkynyl ketones

Both chlorines of 1,1-dichloroethylene (340) react stepwise with different terminal alkynes to form the unsymmetrical enediyne 341 [250]. The coupling of the dichloroimine 342 with tin acetylide followed by hydrolysis affords the dialkynyl ketone 343[2511. The phenylthioimidoyl chloride 344 undergoes stepwise reactions with two different tin acetylides to give the dialkynylimine 345[252],... 

Dialkynyl ketones.1 In the presence of Cl Pd[P(C6H5),]2 1 couples with al-kynyltin compounds (2) to give (N-phenyl)dialkynylimines (3) in 30-75% yield. These products are hydrolyzed to dialkynyl ketones (4) by aqueous acetone (BF, etherate) in —60% yield. Under the same conditions, Grignard reagents undergo coupling to alkanes. 

Dialkynyl ketones react with RhCl(PPh3)3 affording conjugated diynes together with Rh(CO)Cl(PPh3)2. Insertion of rhodium between the carbonyl carbon and the a sp carbon is likely to occur prior to the decarbonylation [41]. 

Not only dialkynyl ketones but also dialkynylphosphine oxides could be employed for this process. Enantioenriched [7]- and [9]helicene-like molecules, containing a densely substituted phosphafluorene core, were synthesized successfully by the inter-molecular double [2 -I- 2 -I- 2] cycloaddition of phenol- or naphthol-linked tetraynes with dialkynylphosphine oxides in the presence of the cationic rhodium(I)/(/ )-Hg-BINAP or (i )-tol-BINAP catalyst (Scheme 10.22) [21]. 

The Sonogashira reaction is of considerable value in heterocyclic synthesis. It has been conducted on the pyrazine ring of quinoxaline and the resulting alkynyl- and dialkynyl-quinoxalines were subsequently utilized to synthesize condensed quinoxalines [52-55], Ames et al. prepared unsymmetrical diynes from 2,3-dichloroquinoxalines. Thus, condensation of 2-chloroquinoxaline (93) with an excess of phenylacetylene furnished 2-phenylethynylquinoxaline (94). Displacement of the chloride with the amine also occurred when the condensation was carried out in the presence of diethylamine. Treatment of 94 with a large excess of aqueous dimethylamine led to ketone 95 that exists predominantly in the intramolecularly hydrogen-bonded enol form 96. 

Addition of P—H bonds to unsaturated systems also continues to be used as a route to heterocyclic systems. Thus base-catalysed cyclization of the phosphine (32) [prepared by the addition of methyl methacrylate (2 moles) to phenylphosphine], followed by subsequent hydrolysis and decarboxylation, affords the phosphorinanone (33). The phosphorinanone system is also directly accessible by the addition of phenylphosphine to divinyl ketones.28 The radical-initiated addition of phenylphosphine to dialkynyl systems (34) gives the heterocyclohexadienes (35).29 80 The stereochemistry of the addition of phenylphosphine to cyclo-octa-2,7-dienone to give... 

Conjugated diynes can also be prepared by decarbonylation of the corresponding diethynyl ketones using (PPhjjjRhCl in boiling xylene (equation 14). High temperatures may be needed to produce the intermediate dialkynyl-rhodium complex. 

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