Cascade rearrangements

Streith J., Defoin A. Aza Sugar Syntheses and Multi-Step Cascade Rearrangements Via Hetero Diels-Alder Cycloadditions With Nitroso Dienophiles Synlett 1996 189-200... 

Further, a very recent paper has reported a cascade rearrangement, under acidic conditions of the simpler educt, a dispiro[3.0.3.3]undecane derivative 93 to the dehydrated isomeric propellane 94 40). It is somewhat reminiscent of the analogous case of 26 where silver ion is the catalyst10). Treatment of the dispiro-alcohol 78 when heated for 2 hrs at 70 °C with p-toluenesulfonic acid in benzene gives in quantitative yield the [3.3.3]propellene 94. The following cascade is proposed to explain the rearrangement. 

Arylazo-4-(3-ethoxycarbonylureido)furoxans 62, which were synthesized by the reactions of 4-amino-3-arylazo-furoxans with ethoxycarbonyl isocyanate, were subjected to cascade rearrangements under the action of potassium r/-butoxidc in dimethylformamide or by heating in dimethyl sulfoxide to form 4-amino-2-aryl-5-nitro-2//-l,2,3-triazoles 63 (Scheme 13) <2001MC230, 2003RCB1829>. 

A novel approach to 1,2,4-thiadiazoles 112 is based on the monocyclic and cascade rearrangement of 1,2,5-oxadiazole-2-oxides 111 <2004PAC1691>. Thus, /V-oxidcs 110 upon treatment with ethoxycarbonyl isothiocyanate undergo cascade rearrangement to give 1,2,4-thiadiazoles 112 via intermediate 111 (Scheme 13). 

The cascade rearrangement of 4-acetoxy-9-furylnaphtho[2,3-, ]furans in ethanol saturated with hydrogen chloride gas gives the tetracyclic naphthodifuran derivatives in moderate yields (Equation 93) <2006TL4117>. The reaction is thought to proceed via double recyclization of both furan rings of the initial molecule (Table 6). 

Table 6 Cascade rearrangement of 4-acetoxy-9-furylnaphtho[2,3-fa]furans...

It must be pointed out that the 1,2-alkyl shift may be subverted by other factors such as steric strain. Thus the cascade rearrangement of a tetraspiroketone on exposure to acid is most aesthetically appealing and synthetically useful for entry into [4.5]coro-nane [201],... 

The fact that both the stereochemistry and the substitution pattern of the sugar anomeric center is conserved allowed to realize a direct transformation of a hex-5-enopyranosides of sucrose 20 into a carba-disaccharide analogue 21 (Scheme 6), and to achieve cascade rearrangements [45]. 

Wagner-Meerwein Rearrangements in the Context of Tandem and Cascade Rearrangements... 

This mixture was then oxidized and homologation of the resulting ketone provided 136. After hydrogenolysis, methyl 5 a-carba-maltoside was isolated [64]. A characteristic of this method is that the rearrangement is done on the disaccharide itself. This method can thus also lead to carba-oligosaccharides through cascade rearrangements [66]. 

Enders, D., Meyer, O. Diastereo- and enantioselective Diels-Alder reaction of 2-amino-1,3-dienes. Liebigs Annalen 1996, 1023-1035. Streith, J., Defoin, A. Aza sugar syntheses and multi-step cascade rearrangements via hetero Diels-Alder cycloadditions with nitroso dienophiles. Synlett 996, 189-200. 

Paquette, L. A. Cascade rearrangements following twofold addition of alkenyl anions to squarate esters. Eur. J. Org. Chem. 1998, 1709-... 

Steinhardt SE, Silverston JS et al (2008) StereocontroUed synthesis of Z-dienes via an unexpected pericyclic cascade rearrangement of 5-amino-2, 4-pentadienals. J Am Chem Soc 130 7560-7561... 

Han GF, Liu YX, Wang QM. Total synthesis of phenanthroindolizidine alkaloids through an amidyl radical cascade/rearrangement reaction. Org Lett 2013 15 (20) 5334-7. 

This type of rearrangement can also occur as a consequence of in situ formation of a suitable intermediate, such as in the case of tandem or cascade reactions. Examples of the isoxazole-to-oxazole rearrangement have been studied both computationally and experimentally, providing evidence of the involvement of a 1,2,4-oxadiazole intermediate (2009JOC351). Synthetically useful cascade rearrangements have also been reported for the one-pot synthesis of indazoles (2011SL3018) and a series of isoxazolo-pyrimidines (2011OL4749). 

Recently, an in-depth theoretical study of this pericyclic cascade rearrangement was performed by Houk and coworkers [49]. Although the mechanistic picture illustrated in Scheme 6.28 seems to be plausible and is in accordance with experimental details, it suffers from energetic barriers that appear too high to allow... 

The third pattern was developed by Paquette, who studied the possibiUty of the concerned reaction extensively and established the cascade rearrangements route [72]. The scenario of the cascade rearrangement is ... 

The cascade rearrangements following double addition of alkenyl anions to the squarate ester was initiated by Paquette from the clue of Asensio s finding that twofold addition of organolithium (MeLi, PhLi, etc.) leads to the facile electrocyclic ring opening to 1,4-diketones [102]. This expedient method for construction of complex polycycles is achieved by a simple one-pot process... 

Scheme 19 Dissected cascade rearrangements with 2-lithiodihydrofuran as an alken d...

A benzyl Claisen cascade rearrangement of keteniminium salts leads to a-arylated lactones in the presence of Tf20, collidine (Scheme 14). ... 

Computational studies of the cascade rearrangements of the cubylcarbinyl radical have been reported. There is evidence for a free-radical pathway under kinetic entropy control for an exocyclic [l,3]-benzyl shift observed in iminium salts derived from... 

A cascade rearrangement of furans to cyclopentenones with congested vicinal stereogenic centres with high diastereoselectivity has been reported to occur through a 4 r-electrocyclization process (Scheme 170). " ... 

Enantioselective cascade rearrangement of enediynes may be achieved using mesoporous silica grafted with a tertiary amine as a basic nanocatalyst. Its action is based on the phenomenon of the memory of chirality [302]. 

Nechab, M., Besson, E., Campolo, D., et al. (2011) An efficient and recyclable hybrid nanocatalyst to promote enantioselective radical cascade rearrangements of enediynes. Journal of the Chemical Society, Chemical Communications, (47), 5286-5288. 

An intramolecular Rh(I)-catalysed formal trawi-bis-silylation across an ortho-positioned C=C bond, as in (170), has been reported (Scheme 9). The reaction is believed to proceed via the initial insertion of Rh into the Si-Si bond to form (171), followed by an intramolecular addition generating (172), which then undergoes a cascade rearrangement via (173) and (174) to produce (175), from which the final 3-silyl-l-benzosilole (176) is obtained upon reductive elimination of [Rh]. ... 

---