Intermediates current multiplication

Propylene oxide (PO) is a major bulk chemical that is useful as an intermediate for the production of glycols, polyethers and polyols. World PO production is about 7 million tons per year, with the market growing by approximately 5% annually. PO comes from two current industrial processes the chlorohydrin process and the organic hydroperoxide process (Scheme 3.1). These processes require multiple steps and suffer from the additional drawback of not producing the desired PO alone. 

Here, we shall focus on ruthenium-catalyzed nucleophilic additions to alkynes. These additions have the potential to give a direct access to unsaturated functional molecules - the key intermediates for fine chemicals and also the monomers for polymer synthesis and molecular multifunctional materials. Ruthenium-catalyzed nucleophilic additions to alkynes are possible via three different basic activation pathways (Scheme 8.1). For some time, Lewis acid activation type (i), leading to Mar-kovnikov addition, was the main possible addition until the first anfi-Markovnikov catalytic addition was pointed out for the first time in 1986 [6, 7]. This regioselectiv-ity was then explained by the formation of a ruthenium vinylidene species with an electron-deficient Ru=C carbon site (ii). Although currently this methodology is the most often employed, nucleophilic additions involving ruthenium allenylidene species also take place (iii). These complexes allow multiple synthetic possibilities as their cumulenic backbone offers two electrophilic sites (hi). 

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