Alkenyl propargyl acetates

The phosphine (127)-catalysed asymmetric 4 +1-cycloaddition reaction of Morita-Baylis-Hillman carbonates with dicyano-2-methylenebut-3-enoates formed highly functionalized cyclopentenes in high yields and excellent ee% The [RuCl(CO)2]2-catalysed 4 + 1-cycloaddition reaction of alkenyl propargyl acetates, RCH(OAc)C=CC(Me)=CH2, with CO in CH2CI2 produced highly functionalized cyclopentenones in high yields (96%). The chiral copper/Tol-BINAP complex... 

The reaction of propargylic chiral acetals with a catalytic copper reagent (RMgX/5% CuX) provides the expected alkoxy allenes in quantitative yield (Table 3)61. The diastereomeric excess is highly dependent on the size of the ring of the acetal and on the type of substituents it contains. The best diastereomeric excess is 85% with the acetal derived from cyclooctanediol. The use of lithium dimethylcuprate results in 1,2-addition lo the triple bond and the resulting lithium alkenyl cuprate bearing a cyclic acetal does not eliminate even at reflux temperature ( + 35°C). 

Enynes which have the secondary or tertiary center at the propargylic position are isomerized to 2-alkenyl-methylenecyclopentane in moderate to high yield with a catalytic amount of [CpRu(CH3CN)3]PF6 in acetone or dimethylformamide (DMF) [25], This catalyst system is acidic, and an acid-labile group such as a dimethyl acetal 54 is hydrolyzed to aldehyde 55. 

Analogous to the allylation with allylsilanes and -stannanes, the transformations, vinylallylation, propargylation, allenylation, alkenylation, alkynylation, and arylation, are viable by the use of an appropriate reagent in the presence of a titanium Lewis acid these are surveyed in the review articles cited both in the Introduction and in this section. The stereochemistry of the reaction of a (vinylallyl)silane in the presence of TiCU has been reported [234]. Equation (113) shows that the major reaction of this silane and isobutyraldehyde occurred mainly in the anti sense with a ratio of anti to syn attack of 90 10 at the terminus remote from the silyl group. Essentially the same stereochemical outcome was observed for the same reaction with the corresponding trimethylsilyl derivative. The intramolecular reaction with an acetal, however, proceeded less selectively the anti syn ratio was 60 40 (Eq. 114) [234]. 

Methyl-, hydroxyethyl-, hydroxypropyl-, and carboxymethyl starches, starch acetates, succinates, alkenyl succinates (Fig. 2), adipates, and phosphates, are all well-known products. Furthermore, special derivatives have also been prepared, such as vinyl-, silyl-, ° or propargyl starches, as reactive intermediates for fiirther fime-tionalization. Unusual substitution patterns can also be established by highly selective deacetylation with alkyldiamines and subsequent introduction of such functional groups as sulfates. From die analytical point of view, the most important aspects are stability under alkaline (mediylation) and acidic or Lewis-acidic (depolymerization) conditions, reactivity (such as migration, rearrangement, further substitution or addition reactions, or any intramolecular reaction), and polarity (lipophilic/hydrophilic, ionic/nonionic, acidic/basic). These properties mainly determine the analytical... 

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