Carbonic acid esters triple bonds

Propargylic alcohols are also very interesting because anti-Markovnikov addition of benzoic acid generates bifunctional 1,3-hydroxy esters with addition of the car-boxylate to the terminal carbon of the triple bond [14, 15]. This reaction contrasts... 

Addition of carbonic acid esters to carbon-carbon triple bonds s. 13, 327 Aluminum isopropoxide Al(OR) ... 

When the nitrogen atom of a pyridine is sufficiently nucleophilic, for example 3-cyano- (pK 1.45) but not 3-bromopyridine (pATa 0.9), attack occurs at the triple bond of the ester.238 The reaction can be very vigorous and, if carried out at - 60° in ether, pyridine itself appears to yield the zwitterion 1 which can be trapped by carbon dioxide. No direct physical evidence has been obtained for 1 and the first product detectable by low-temperature NMR measurements is the 9a//-quinolizine 5.239 Both geometrical forms of the betaine (2) have been isolated, and, at 0° in chloroform, decomposition to carbon dioxide, detected by its absorption at 2335 cm-1, and a red tar, occur rapidly. Treatment of the betaines with aqueous perchloric acid at its freezing point, however,... 

Step 5 of the mechanism shown in Figure 16.35 (part II) is new. It consists of the cw-selec-tive addition of the aryl-Pd complex to the C=C double bond of the acrylic acid methyl ester, i.e., a carbopalladation of this double bond. A related reaction, the cw-selective car-bocupratlon of C=C triple bonds, was mentioned in connection with Figure 16.17. The regioselectivity of the carbopalladation is such that the organic moiety is bonded to the methylene carbon and Pd to the methyne carbon of the reacting C=C double bond. The addition product is an alkyl-Pd(II) complex. 

The same research group has also developed the ruthenium-catalyzed inter-molecular addition of carboxylic acids to carbon-carbon triple bonds [4]. When a-hydroxy acids 3 were employed with terminal alkynes, 1,3-dioxolan-4-ones 5 were synthesized via cyclization of enol ester intermediates 4 (Eq. 2) [5]. 

Three important processes have evolved from Reppe s work. Vinylation, the formation of vinyl derivatives by reaction of such compounds as acids, glycols, and alcohols with acetylene, produces the important vinyl esters and vinyl ethers. Ethinylation is defined as the reaction of acetylene with the carbon atom of a reactant without loss of the triple bond. A major application of the ethinylation reaction is to aldehydes and ketones to give alkynols and alkyndiols—e.g., the reaction of acetylene with formaldehyde to give propargyl alcohol and butyn-2-diol-l,4. Carboxylation (also referred to as carbonylation), the reaction of acetylene with carbon monoxide in the presence of metal carbonyls, has been applied to the production of acrylic acid, acrylates, and hydroquinone. 

Hydrocarboxylation is the formal addition of hydrogen and a carboxylic group to double or triple bonds to form carboxylic acids or their derivatives. It is achieved by transition metal catalyzed conversion of unsaturated substrates with carbon monoxide in the presence of water, alcohols, or other acidic reagents. Ester formation is also called hydroesterification or hydrocarb(o)alkoxylation . The transition metal catalyst precursors are nickel, iron or cobalt carbonyls or salts of nickel, iron, cobalt, rhodium, palladium, platinum, or other metals4 5. 

---