Dihydronaphthalenes rearrangement

Dihydronaphthalenes are remarkable substrates for the combined C-H activation/Cope rearrangement, but under certain circumstances, further cascade reactions can occur. This was seen in the Rh -DOSP -catalyzed reaction of vinyldiazoacetate 26 with dihydronaphthalene 25 (Equation (35)).96 In this case, the isolated product was the formal C-H insertion product. The reaction proceeded through a combined C-H activation/Cope rearrangement to form 27, followed by the reverse Cope rearrangement. As both steps were highly stereoselective, the formal C-H insertion product 28 was produced with very high stereoselectivity (>98% de, 99.6% ee).96... 

Specific acid-catalysed solvolysis of l-methoxy-l,4-dihydronaphthalene or 2-methoxy-l,2-dihydronaphthalene in 25% acetonitrile in water has been found to yield mainly the elimination product, naphthalene, along with a small amount of 2-hydroxy-1,2-dihydronaphthalene, there being no trace of either the 1-hydroxy-1,4-dihydronaphthalene or the rearranged ether. The nucleophilic selectivity, ns/ hoh = 2.1 X 10", between added azide ion and solvent water has been estimated for the relatively stable = 1 x 10 s ) intermediate benzallylic carbocation for which the barrier to dehydronation is unusually low k = 1.6 x 10 ° s ), as evidenced by the large elimination-to-substitution ratio with solvent water as base/nucleophile. The kinetics of acid-catalysed solvolysis of 1-hydroxy-1,4-dihydronaphthalene and 2-hydroxy-1,2-dihydronaphthalene have also been studied. 

A minimal structural feature for di-rr-methane rearrangement of acyclic arylpropenes to occur in solution appears to be the presence of an additional phenyl group.A similar requisite seems valid also for cyclic 1,4-systems such as indenes, while the scope for 1,4-dihydronaphthalenes is uncertain. 

The various stages in the hydrogenation process are well defined the 1,4-dihydronaphthalene is produced first, but as this is not one of the more stable forms, an exothermic molecular rearrangement occurs with the formation of i, 2-dihydronaphthalene ... 

Acyl esters of vicinal diols are obtained by the reaction of alkenes with metal carboxylates [436]. Lead tetraacetate in acetic acid at 70 °C converts 1,2-dihydronaphthalene to rranj-l,2-diacetoxy-l,2,3,4-tetrahy-dronaphthalene in 72% yield [436]. The reaction is not always stereospecific. Cyclohexene treated with thallium triacetate gives a mixture of diastereomers in varying ratios, depending on reaction conditions, and byproducts as a result of rearrangements (equation 89) [411],... 

Similar rearrangements were carried out with 3, 4 -dihydrospiro[cyclopropane-l,l (2 -naph-thalen]-2 -yl methyl oxalates 48, which gave good yields of 4-ethyl-1,2-dihydronaphthalenes... 

In contrast to the parent cydopropa[a]naphthalene, its 1,1-dichloro- and 1.1-difluoro derivatives may be synthesized by a variation of the original Billups scheme. The respective dihalocar-benes were added to l-bromo-3,4-dihydronaphthalene. A bromo substituent was then introduced at C3 of 7 by benzylic bromination with 7V-bromosuccinimide, after which aromatization to the very labile cycloproparene products 8 was elTected under mild conditions. In this sequence, the halogens were situated in such a way that no exocyclic double bonds could be formed upon dehydrobromination. The problem of rearrangement of such a double bond into the six-membered ring is therefore circumvented. Both the dichloro and the difluoro derivatives 8 are very sensitive to moisture, and have only been observed in solution. 

After the discovery of this unique transformation, the scope was explored. When certain 1,2-dihydronaphthalene substrates 158 were utilized, it was found that the direct C-H insertion products 161 were formed in extraordinarily high diastereose-lectivity and enantioselectivity (>98 de and >95 ee, Scheme 38), much higher than was typically observed for insertion reactions with aryldiazoacetates (see Sect. 3.2). Thus, it was reasoned that these compounds were actually being produced via a combined C-H activation/Cope rearrangement, through a transition state such as 162, followed by a retro-Cope. Furthermore, appropriate substrate modification allowed isolation of the C-H activation/Cope adduct 160, providing products in >98% de and up to >99% ee [112, 113]. In certain cases, a double C-H insertion into dihydronaphthalene substrates was also observed [112],... 

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