Alkynyl ketones cycloaddition

Obrecht, D., Zumbrunn, C., Mueller, K. Formal [3+2] Cycloaddition Reaction of [1,4]Oxazin-2-ones and a-Alkynyl Ketones via a Tandem Mukaiyama-Aldol Addition/Aza-Cope Rearrangement. J. Org. Chem. 1999, 64, 6891-6895. 

Another example of a [4S+1C] cycloaddition process is found in the reaction of alkenylcarbene complexes and lithium enolates derived from alkynyl methyl ketones. In Sect. 2.6.4.9 it was described how, in general, lithium enolates react with alkenylcarbene complexes to produce [3C+2S] cycloadducts. However, when the reaction is performed using lithium enolates derived from alkynyl methyl ketones and the temperature is raised to 65 °C, a new formal [4s+lcj cy-clopentenone derivative is formed [79] (Scheme 38). The mechanism proposed for this transformation supposes the formation of the [3C+2S] cycloadducts as depicted in Scheme 32 (see Sect. 2.6.4.9). This intermediate evolves through a retro-aldol-type reaction followed by an intramolecular Michael addition of the allyllithium to the ynone moiety to give the final cyclopentenone derivatives after hydrolysis. The role of the pentacarbonyltungsten fragment seems to be crucial for the outcome of this reaction, as experiments carried out with isolated intermediates in the absence of tungsten complexes do not afford the [4S+1C] cycloadducts (Scheme 38). 

Thus far, the [5 + 2 + 1]-reaction works efficiently with alkynyl esters, amides, aldehydes, and ketones or an alkynyl-substituted allene44 as the two-carbon component (Scheme 58). Just as in the case of the [5 + 21-cycloaddition of VCPs and allenynes, the [5 + 2 + l]-reaction is selective for the allene over the alkyne subunit (Equation (35)). 

The AuCl-catalysed 4 + 2-cycloaddition of benzyne with o-alkynyl(oxo)benzenes produced anthracene derivatives having a ketone in the 9-position, in good to high yields under mild conditions.118 Hypervalent iodine compounds, [5-acyl-2-(trimethyl-silyl)]iodonium triflates, readily yielded acylbenzynes which could be trapped with furan.119 Both DMAD and benzyne reacted with borabenzene to yield substituted borabarrelenes and borabenzobarrelenes, respectively.120... 

Simple a,3-unsaturated aldehydes, ketones, and esters (R = C02Me H > alkyl, aryl OR equation l)i, 60 preferentially participate in LUMOdiene-controlled Diels-Alder reactions with electron-rich, strained, and selected simple alkene and alkyne dienophiles, - although the thermal reaction conditions required are relatively harsh (150-250 C) and the reactions are characterized by the competitive dimerization and polymerization of the 1-oxa-1,3-butadiene. Typical dienophiles have included enol ethers, thioenol ethers, alkynyl ethers, ketene acetals, enamines, ynamines, ketene aminals, and selected simple alkenes representative examples are detailed in Table 2. - The most extensively studied reaction in the series is the [4 + 2] cycloaddition reaction of a,3-unsaturated ketones with enol ethers and E)esimoni,... 

To date, four bioorthogonal reactions have been used to label glycans on cells and in lysates hydrazone/oxime formation with ketones, thiol alkylation with maleimides, Staudinger ligation of azides with triaryl phosphines, and copper-catalyzed or strain-promoted [3+2] cycloadditions of alkynes and azides (Figure 5) (25, 26, 32, 34, 35). While each reaction has been used extensively, most recent applications have employed azido- or alkynyl-sugars due to their superior metabolic incorporation and efficient ligations. 

Cycloaddition. 1-Alkynyl-l-cyclopropyl ketones generate cyclic 1,3-dipolar species and their cycloaddition with vinyl ethers is followed by ring size regulation of the cycloadducts (expansion of the 3-membered ring and contraction of the 6-membered ring) and... 

A new chiral sulfinamide monophosphine hgand was used in an asymmetric gold(l)-catalyzed formal [4 + 3] cycloaddition reaction between a l-(l-alkynyl)cyclopropyl ketone and a nitrone to give cycloadduct 91 in 94% yield and 89% ee (14AGE4350). 

Formation.—Phenyl-, 2-naphthyl-, 2-thienyl-, and 2-furanyl-thiets are prepared from aryl methyl ketones, dimethylamine, and methanesulphonyl chloride. X-K y crystal structures establish that the compounds arising from the cycloaddition of alkynes to thioxanthones are thiets, and not spiro-dihydropyrans, as originally proposed. Additional work shows that alkynyl sulphides also give thiets with thioxanthone, and that the adduct (104) is in rapid equilibrium with the open form (105) in solution, although they can be isolated separately. Thiet (106) was isolated after thermolysis of a Dewar thiophen—azide adduct. ... 

Abstract The use of organoaluminum-based Lewis acids (A1R X3 R = alkyl, alkynyl, X = halide or pseudohalide) in the period 2000 to mid-2011 is overviewed with a focus on (1) stoichiometric reactions in which one of the organoaluminum substituents is transferred to the substrate (e.g., the opening of epoxides, 1,2-additions to carbonyl compounds, coupling with C-X, and Reissert chemistry) and (2) asymmetric, often catalytic, reactions promoted by Lewis acid catalysts derived from organoaluminum species (e.g., use of auxiliaries with alanes, Diels-Alder, and related cycloaddition reactions, additions to aldehydes and ketones, and skeletal rearrangement reactions). 

Bromo-levoglucosenone 31 provides a functionalized dienophile which undergoes cycloaddition to give, after straightforward manipulation, ketone 32. The hindered ketone unit of 32 underwent nucleophilic attack using an alkynylborate complex in a synthetic approach directed towards tetrodotoxin (Scheme 6). Ketone 32 was found to be extremely sensitive and the precise nature of the alkynyl nucleophile was crucial to the success of the key addition step. ... 

---