Olefin-directed couplings

The direct methane conversion technology, which has received the most research attention, involves the oxidative coupling of methane to produce higher hydrocarbons (qv) such as ethylene (qv). These olefinic products may be upgraded to Hquid fuels via catalytic oligomerization processes. 

Other approaches to direct C2Q couplings have been reported (9,30—35). Based on their knowledge of sulfone chemistry, Rhc ne-Poulenc has patented many syntheses of P-carotene which use this olefination chemistry (36—41). Homer-Emmons chemistry has also been employed for this purpose (42). The synthetic approaches to the carotenoids have been reviewed (43). 

Reduction of the catalyst/hydrocarbon time in the riser, coupled with the elimination of post-riser cracking, reduces the saturation of the already produced olefins and allows the refiner to increase the reaction severity. The actions enhance the olefin yields and still operate within the wet gas compressor constraints. Elimination of post-riser residence time (direct connection of the reactor cyclones to the riser) or reducing the temperature in the dilute phase virtually eliminates undesired thermal and nonselective cracking. This reduces dry gas and diolefin yields. 

Oxalamidinate anions represent the most simple type of bis(amidinate) ligands in which two amidinate units are directly connected via a central C-C bond. Oxalamidinate complexes of d-transition metals have recently received increasing attention for their efficient catalytic activity in olefin polymerization reactions. Almost all the oxalamidinate ligands have been synthesized by deprotonation of the corresponding oxalic amidines [pathway (a) in Scheme 190]. More recently, it was found that carbodiimides, RN = C=NR, can be reductively coupled with metallic lithium into the oxalamidinate dianions [(RN)2C-C(NR)2] [route (c)J which are clearly useful for the preparation of dinuclear oxalamidinate complexes. The lithium complex obtained this way from N,N -di(p-tolyl)carbodiimide was crystallized from pyridine/pentane and... 

The rule in carbon-13 NMR is that sp2-hybridized carbons (carbonyl, aromatic, olefinic) absorb at lowest field, followed by sp-hybridized (acetylenic, nitrile) and sp3 (aliphatic). A first glance leads us to believe we have seven signals, but we must remember that the methine carbon is directly bonded to phosphorus, so that we shall expect a relatively large C-P coupling. The other C-P couplings will probably be very much smaller. 

The product of the dimerization of an unsymmetrical substituted olefin, such as propene, is dependent on the direction of coupling of the two olefinic units in general, a mixture of isomers is obtained. In order to obtain a high yield of a particular dimer, the control of the regioselectivity of the individual addition steps in the catalytic cycle or even the reversal of the direction of addition in consecutive steps is required (Section IV,E). 

Since the direct carbonylation of C-H bonds with CO leading to aldehydes is endothermic, the reaction is conducted under photochemical conditions.109,109a 109e On the other hand, the direct coupling of a C-H bond, CO, and an olefin leading to a ketone is exothermic and can proceed under thermal reaction conditions. 

McMurry, in 1974, introduced as the reducing agent the LiAlH4-TiCl3 couple, in which the active species is probably Ti(II) and which allows the coupling of ketones to afford directly the corresponding olefin in good yields [31]. 

Marcus, D.M., McLachlan, K.A., Wildman, M.A., Ehresmann, P.W., and Haw, ).F. (2006) Experimental evidence from H/D exchange smdies for the failure of direct C-C coupling mechanisms in the methanol-to-olefin process catalyzed by HSAPO-34. Angew. Chem. Int. Ed., 45, 3133-3136. 

In the 1990s, the groups of Hiemstra and Larock independently discovered that Pd(OAc)2 in DMSO serves as an effective catalyst for direct dioxygen-coupled catalytic turnover, and this catalyst system was applied widely to oxidative heterocyclization reactions. Examples include the addition of carboxylic acid, phenol, alcohol, formamide, and sulfonamide nucleophiles to pendant olefins (Eq. 26) [146-149]. 

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