Heck experimental procedures

There are certain metrics used in Green Chemistry. One is associated with principle two Synthetic methods should be designed to maximize the incorporation of all materials used in the process into the final product. That is the metric of atom economy [14]. Atom economy is the mass of the product divided by the sum of the mass of all the reactants. Ideally this number is one and the closer to one the better. Atom economy does not take into account solvent or other reagents such as bases. Another metric is the Environmental factor or E-factor [15], The E-factor is the mass of the total waste divided by the mass of the product. Ideally the E-factor should be zero and the smaller the number, the better. However, some fine chemical or pharmaceutical syntheses have E-factors of about one hundred. Using micelles, the Lipshutz group reduced the E-factor of a Heck reaction from 137 to 7.5 and then even lower with recycle [16], Consider the following experimental procedure [17],... 

The second standard protocol makes use of the so-called Jeffery conditions containing a solid phase-transfer catalyst, e.g., tetrabutylammonium chloride. In addition, a solid base such as sodium carbonate or sodium acetate in A,A -dimethylformamide (DMF) is used at a somewhat lower temperature in comparison to Heck conditions (Experimental Procedure below). 

In case of allyl alcohols, the Heck reaction delivers the corresponding propionaldehydes (Experimental Procedure below). 

The intra-intermolecular Heck reaction of dienediol bisnonaflates containing an (O-alkenyl substituent with an external alkene such as an acrylate gives rise to the formation of a bicyclic tetraene by an intramolecular coupling followed by an intermolecular Heck or Sonogashira-type reaction (Scheme 5-30, Experimental Procedure below).It should be noted that the alkynylation proceeds in absence of copper additives. 

In addition, acyclic enantiotopic double bonds can be differentiated by using an asymmetric Heck reaction (Experimental Procedure below typical procedure for desymmetrizing Heck cyclizations). ... 

Most of the substrates discussed before feature sp or sp -hybridized carbon atoms connected to the leaving groups. However, there are some reports indicating that some sp -hybridized substrates undergo Heck-type reactions. At least in some cases, radicals or cationic species are involved. For example, 1-bromoadamantane derivatives react with alkenes under palladium catalysis to give rise to 1-adamantyl alkenes (Scheme 5-39) (Experimental Procedure below). 

As noted in the paragraph dealing with diazonium salts in the Heck reaction, diazonium salts are versatile starting materials for cross-coupling reactions. Recently, Schmidt and co-workers used the Suzuki coupling in the presence of diazonium salts (Experimental Procedure below). 

The homo-coupling of terminal alkynes is a frequent side reaction in Sonogashira and Heck-type alkynylation reaction. However, this reaction can be optimized to obtain Glaser-type products in good yields. The power of this reaction has been demonstrated in the synthesis of a wheel-like structure by Hoger and colleagues (Experimental Procedure below). ... 

There are ample examples for pure domino Heck reactions. For example, ortho-bromostyrenes can be coupled with a long range of olefins as relays to give substituted indenes (Experimental Procedure below). " ... 

Even bromodienes with methylenecyclopropane terminators undergo smooth Heck reactions (Scheme 5-210). The concomitant Diels-Alder reaction is regioselective and is leading to one spirobicyclo[4.3.0]nonane. In all cases, silver ions prevent double-bond migration of the intermediate diene (Experimental Procedure below). High-pressure conditions facilitate both the Diels-Alder reaction and the cross-... 

---