Dihydrofurans, rhodium-catalyzed

Dilithio-1,3-dienes were found to react with aldehydes to form polysubstituted 2,5-dihydrofurans in a regio- and stereoselective manner <02OL2269>. Like other metal-carbene reactions, rhodium-catalyzed tandem carbonyl ylide formation - cycloaddition with propargyl bromide gave the 2,5-dihydrofuran in good yield <020L1809>. 

As represented in Equation (122), a rhodium-catalyzed hydroformylation of 2,3- and 2,5-dihydrofuran using furanoside-derived chiral diphosphite ligands, for example, 237, provided 3-formyltetrahydrofuran as the major product with ee up to 75% <2005CC1221>. 

Also norbomene and related systems, as well as dihydrofuranes, have been hydrosilated with good enantioselectivities with similar MOP ligands. Intramolecular rhodium catalyzed asymmetric hydrosUations have been achieved with good enantioselectivities, for example with meso- or other allylsilylethers. ... 

Usually unsaturated functionalized cyclic alkenes such as dihydrofurans [27] and N-acyl-2-pyrrolines [23] are also very reactive towards rhodium-catalyzed hydroformylation. They principally give the expected a-formyl... 

Cycloinumakiol is a diterpene isolated from podocarpus latifolius. The originally proposed structure was 36 with a tetracyclic dihydrofuran skeleton having a quaternary chiral carbon center at the benzylic position (Scheme 8.6). Dong et al. developed a rhodium-catalyzed site-selective alkene insertion reaction into a C-C bond of benzocyciobutenones [24], and applied it to the first total synthesis of 36 [25]. The synthesis led to the structural revision of cycloinumakiol. 

It was described earlier in this book chapter that the rhodium-catalyzed intramolecular C-H insertion reaction of metal carbenoids (mainly produced from diazocarbonyl compounds) is useful for the construction of natural products containing a dihydrofuran core (see details in Sections 16.2.4.4 and 16.2.4.5). C-H insertion using achiral or chiral rhodium(II) catalysts was also used to construct pyrrolidine frameworks, with representative applications to the synthesis of natural products and pharmaceuticals shown in Figure 16.3 [88]. 

Dihydrofuran derivatives 319 are formed as major products in Rh2(OAc)4-catalyzed reactions of a-diazoacetophenone with 2-methoxy-propene or a-methoxystyrene (84MI1). Copper chelate or rhodium(II) acetate-catalyzed 1,3-dipolar cycloaddition of metal carbenoids, generated from ethyl formyldiazoacetate (90JOC4975), ethyl diazopyruvate... 

Boyer, A. Rhodium(lI)-catalyzed stereocontroUed synthesis of dihydrofuran-3-imines from l-Tosyl-l,2,3-triazoles. Org. Lett. 2014, 16, 1660-1663. 

Wang Y, Zhu S (2(X)1) A simple synthesis of fluoroaJkyl substituted dihydrofurans by rhodium(II)-catalyzed 1,3-dipolar reactions. Tetrahedron 57 3383-3387... 

The Ma group has reported some very elegant multibond forming processes to synthesize dendralenes, including both palladium(II)- and rhodium(I)-catalyzed cycloisomerizations of di-allenes 106 to form cyclic dendralenes 107 (Scheme 1.15) [68, 69, 71], and also the remarkable palladium(0)-catalyzed three-component reaction of di-allenes 108, propargylic carbonates 109, and boronic acids 110 to form bicyclic [3]dendralenes 111 (Scheme 1.15) [70]. Similar, intermolecular transformations to those used to form dendralenes 107 had been reported earlier by Alcaide, to synthesize dihydrofuran-containing dendralenes [72, 73]. 

Chikkali SH, Bellini R, Berthon-Gelloz G, van der Vlugt JI, Bruin B, Reek JNH. Highly enantioselective hydroformylation of dihydrofurans catalyzed by hybrid phosphine-phos-phonite rhodium complexes. Chem. Commun. 2010 46 1244-1246. 

---