C/s-addition

A wide variety of heterocycles can be readily prepared by the heteroannulation of alkynes. For example, the palladium-catalyzed annulation of internal alkynes by 2-iodoanilines provides easy access to 2,3-disubstituted indoles by a process that involves initial reduction of Pd(OAc)2 to Pd(0), oxidative addition of the aryl halide to Pd(0), c/s-addition of the arylpalladium... 

These results, which correspond to stereospecific cis addition of hydrogen to the double bond, stand in direct contradiction to the report st> by Elving and coworkers that dimethylmaleic acid 112, R = H) affords dl-113 (R = H) exclusively and that dimethylfumaric acid affords only meso-113 (R = H). The latter results correspond of course to stereospecific tram addition of hydrogen across the double bond. Camilli, like Homer and R6der, however, observed c/s-addition of hydrogen, albeit in a slightly different system, 18> ... 

Intramolecular c/ s-addition processes with platinum catalysts 805... 

Figure 26. Morphology of measured crystals of (R,Sj-A-acety lvaline. (a) Pure. (b- d) grown in the presence of A-acetylphenylglycine (b) R additive (c) S additive (d) R,S additive.

Cycloaddition of a-nitroso acrylic esters (749) to alkenes followed by base hydrolysis provides a route to 5,6-dihydro-4//-l,2-oxazine-3-carboxylic acids (750). These heterocycles on heating above 150 °C decarboxylate to furnish y-hydroxynitriles (thus the overall c/s-addition of OH and CH2CN to a double bond), which can be transformed further to y-lactones (751) by treatment with methanolic hydrochloric acid (Scheme 172) (79CC1090). The adducts were also reduced to a-amino esters (752) by the action of aluminum amalgam (Scheme 173) (79CC1089). 

IR spectra or trapped by oxalyl chloride or water. Furthermore, the isomeric 1,4-substituted A2-tetrazoline-5-thiones, which would have been formed by C=N instead of C=S addition, were definitively excluded by independent synthesis.64... 

Anodic addition of two methoxy groups across the double bond of cis- and frans-stilbene has been shown to occur with a slight preference for c/s-addition 58 104 again adsorbed intermediates were suggested to play an important role (Eq. (34)). 

The incorporation of [3H]MVA into phospholipids in hamster liver in vivo has been claimed,380 and a possible intermediate, which had similar properties to dolichyl-mannose phosphate, incorporated tracer from tritium-labelled mannose and MV A in the same system. The C45, C50, and C55 polyprenols of leaves of Cleome spinosa that have only three trans double bonds within the molecule are thought381 to be synthesized by successive c/s-addition of isoprene units to all-trans-GGPP. 

Homogeneous model complexes shed light on the reactivity of thiophene and benzothiophene. Thiophene is known to coordinate to metals in if- to -fashion, as in (21-XXIV) to (21-XXVII). The rf-S and rf-C,C structures are believed to act as immediate precursors to C—H and C—S addition reactions. This was confirmed spectroscopically for the reaction of (pp3)Ru(N2) with thiophene ... 

Alkynes insert into M—H and M—C bonds, typically to give c/s-addition products,... 

Carbozincation of alkynes. A dialkylzinc in combination with I2ZrCp2 undergoes regioselective c/s-addition to terminal alkynes to provide alkenylzinc derivatives (equation I). The reaction is catalytic in I2ZrCp2, but at least 1 equiv. of I2ZrCp2 is required for satisfactory results. Cl2ZrCp2 or Br2ZrCp2 is less effective.1... 

A structure determination showed c/s-addition . Thiol oxidative addition and coordination were shown in the same iridium(III) complex . 

CiftLi, C4oLi C24K, CjjK 30 butadiene More 1,2-addition and some 1,4-c/s-addition. Low temp, favours 1,2-addition ... 

Homogeneous hydrogenation catalyst. Acetylenes can be reduced stereospecific-ally to trans-olefins by the reagent in THF or diglyme. In one experiment conducted in toluene, c/s-addition was observed.37... 

Adamantane synthesis, catalyst Aluminum bromide. c/s-Addition to alkynes Diisobutylaluminum hydride. 

The use of dienecarboxylic acids (cf. Section 8.3.1.1, under Intramolecular 1,4-diacyloxylation ) under the conditions for haloacyloxylation in acetone resulted in a highly stereoselective chlorolactonization [Eqs.(44) and (45)] [67]. The reaction proceeds >98% as a 1,4-c/s addition and involves the same intermediate lactone jr-allyl complex as in the intramolecular diacyloxylation. 

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