Petasis/Diels-Alder reaction

More recently. Beau and Norsikian reported remarkable diastereoselective domino Petasis/Diels-Alder reactions of unprotected carbohydrates with allylamines and boronic acids [30]. As shown in Scheme 1.6, free sugars, such as D-ribose and D-fucose, reacted through a three-component reaction to give the corresponding complex heterocyclic chiral domino products in good yields and often complete diastereoselectivity. The domino process started with a Petasis reaction occurring... 

SCHEME 1.6 Three-component domino Petasis/Diels—Alder reactions of unprotected carbohydrates. 

An outstanding example of a branching pathway exploited complementary cyclisation reactions to yield alternative molecular scaffolds (Scheme 1.5). A four-component Petasis condensation reaction was used to assemble flexible cyclisation precursors e.g. 14). Alternative cyclisation reactions were then used to yield products with distinct molecular scaffolds Pd-catalysed cyclisation (- 15a) enyne metathesis (- 15b) Ru-catalysed cycloheptatriene formation (- 15c) Au-catalysed cyclisation of the alcohol onto the alkyne (- 15d) base-induced cyclisation (- 15e) Pauson-Khand reaction 15f) and Miesenheimer [ 2,3]-sigmatropic rearrangement (not shown). Four of these cyclisation reactions could be used again to convert the enyne 15e into molecules with four further scaffolds (17a-d). In addition, Diels Alder reactions with 4-methyl-l,2,4-triazoline-3,5-dione converted the dienes 15b, 17a and 17d... 

Table 2.1 lists some of the mechanistic studies of organic and organometallic reactions reported in the literature by ESI-MS. All sorts of reactions have been successfully explored in the gas phase, such as the Baylis-Hillman reaction [211-213], C-H or N-H activation [214—219], cydopropanation reaction [220], Diels-Alder reactions [221], displacement reactions [222], electrophilic fluorination [223, 224], Fischer indole synthesis [225], Gilman reaction [226, 227], Grubbs metathesis reaction [228-231], Heck reaction [194], methylenation [232], oxidation [233, 234], Petasis olefination reaction [235], Raney Nickel-catalyzed coupling [236], ruthenium... 

Conceptually similar palladium-catalyzed cascade reactions have been developed, involving molecular-queuing cycloaddition, cyclocondensation and Diels-Alder reactions [71], cydization-anion-capture-olefin metathesis [72], carbonylation-allene insertion [73], carbonylation/amination/Michael addition [74], sequential Petasis reaction/palladium-catalyzed process [75], supported allenes as substrates [76], and palladium-ruthenium catalysts [77]. 

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