Step-economical synthesis

Gong and co-workers developed the first step-economical synthesis of the previously described process. The approach involves a Friedlander condensation [88, 89] followed by a transfer hydrogenation catalyzed by a combination of an achiral Lewis acid and a chiral Brpnsted acid. This affords the direct conversion of 2-aminobenzaldehyde derivatives 19 and ketones 23 into highly optically active 1,2,3,4-tetrahydroquinoline derivatives 22 and 24, with enolizable dicarbonyl compounds 20 (Scheme 7) [90]. 

Step-Economical Synthesis of Clinprost and Analogs Utilizing a Novel Decarboxylation Reaction... 

Petrignet, J., Boudhar, A., Blond, G., Suffer , J. (2011). Step-economical synthesis of taxol-like tricycles through a palladium-catalyzed domino reaction. Angewandte Chemie - International Edition, 50, 3285-3289. 

Harrison TJ, Ho S, Leighton JL. Toward more ideal polyketide natural product synthesis a step-economical synthesis of Zincophorin methyl ester. J. Am. Chem. Soc. 2011 133 7308-7311 and references therein. 

In all, only six steps are involved, making this a most economical synthesis. Chrysanthemic acid is important enough to have been made in many other ways too (e.g. Tetralredron Letters, 1976, 2441 Bull. Soc. Chim. France, 1966, 3499). 

According to another important and promising technology, hydrocarbons are produced from methanol, which, in turn, is synthesized from synthesis gas. Called the methanol-to-gasoline process, it was practiced on a commercial scale and its practical feasibility was demonstrated. Alternative routes to eliminate the costly step of synthesis gas production may use direct methane conversion through intermediate monosubstituted methane derivatives. An economic evaluation of different methane transformation processes can be found in a 1993 review.1... 

In the second step, the synthesis gas and additional steam are passed over a metal oxide catalyst at about 400°C. Under these conditions, the carbon monoxide component of the synthesis gas and the steam are converted to carbon dioxide and more hydrogen. This reaction of CO with H20 is called the water-gas shift reaction because it shifts the composition of synthesis gas by removing the toxic carbon monoxide and producing more of the economically important hydrogen ... 

Biotech may be gaining importance in the food and nutrition sector, but many nutritional ingredients are still produced by chemical synthesis or via extraction for example, carotenoids are currently most competitively produced by chemical means. For vitamin B2, however, the situation has changed completely in the last five years. The traditional eight-step chemical synthesis has been replaced by one fermentation process. This biotech process, which is also practiced by BASF on a large scale, reduces overall cost by up to 40 percent and the overall environmental impact by 40 percent, as has been shown by detailed life cycle assessments. Similar trends have been described for other bio-based processes, indicating that economic and environmental benefits go hand in hand in today s white biotech practice (EuropaBio and McKinsey Company, 2003, DSM position document, 2004). 

Fischli has described a chiral, economic synthesis of (5)- and (/ )-muscone (119) also starting from (120). The key step is the epoxysulfonyl cyclofragmentation of (123) to ( ,Z)-dehydiomuscone (125 Scheme 40) in a one-pot procedure. The sulfone moiety serves as a carbanion stabilizer for the epoxide cleavage as well as a leaving group. 

Adding a catalytic amount of an alkyne to the reaction in Equation 1.63 indeed enhanced the yield dramatically. The quantitative yield for the activation step obtained using 3-hexyn-l-ol made this alkyne the one of choice as the activator for the allene addition. Taking advantage of this atom economic synthesis of 1,3-dienes by employing the [4 + 2] cydoaddition then allows complex cyclic entities to be available with high atom economy. 

---