1,2-Dihydronaphthalenes, ring

Protonic acids and some other electrophiles cause the aromatization of naphthalen-l,4-imines and of derivatives of the related 1,4-epoxy-1,4-dihydronaphthalene ring system (126) to naphthalene derivatives (see Section III,F), and simple electrophilic addition to the 2,3-double bond has not been observed. Ring-opening of the ether (126) also occurs on addition of alkyl or aryl lithium reagents as a result of exo attack by the nucleophile at the 2-position. ... 

An intriguing copper-catalyzed radical reaction that involves a formal C-H bond activation has been reported by Nakamura. The reaction efficiently couples an arylacetylene or enyne to a penta(aryl)[60]fullerene bromide in a formal [4 -I- 2] fashion to form a dihydronaphthalene ring fused to a fullerene sphere [35]. 

I, 4- and 3,4-Dihydroquinazolines are tautomeric but any attempts to prepare the former w ithout a 1-substituent have led to the latter. The greater stability to proto tropic change of 1,2-dihydronaphthalene over 1,4-dihydronaphthalene is also found in 3,4-dihydroquinazoline. Earlier claims to the preparation of l,4-dihydroquinazolines ° were erroneous and based on incomplete experimental data. The first 1,4-dihydroquinazoline was prepared as recently as 1961. 1-Methyl and l-benzyl-l,4-dihydroquinazolines were obtained from o-methylamino-and o-benzylamino-benzylamines (42) by formylation and ring closure. Attempts to remove the benzyl group gave 3,4-dihydroquinazoline. These 1,4-dihydro compounds are susceptible to oxidation, and attempts made to prepare 1,2-dimethyl-1,4-dihydroquinazoline from o-... 

Our uncertainty is derived in part from the lack of a measured enthalpy of vaporization, cf Reference 67. However, what triggered our skepticism is the observation that the isomeric 1,2-and 1,4-dihydronaphthalenes have reported enthalpies of formation that differ by ca 13 kJ mol-1 while the corresponding species lacking the benzene ring, the isomeric 1,3- and 1,4-cyclohexadienes, are almost isoenergetic (see Section V.D of this chapter). From J. F. Liebman, in The Cyclophanes (Eds. P. M. Keehn and S. M. Rosenfeld), Academic Press, New York, 1983,... 

In the case of p-methoxystyrene (p-MeOCgH4CH=CH2), the cation-radical ring closure can lead to 1,2-dianisylcyclobntane or 4-anisyl-6-methoxy-3,4-dihydronaphthalene. Thermodynamic simulations show that the former should be favored in the absence of a solvent, whereas the latter product could be stabilized by a polar solvent (O Neil and Wiest 2006). Of course, such a solvent has to be fairly polar and not nncleophilic. 

The methodology was extended to an asymmetric introduction of snbstitnents to a naphthalene ring. When chiral naphthyloxazolines 13 were used as substrates, di- or trisubstituted dihydronaphthalenes 15 were obtained in high diastereomeric ratio (dr) after the treatment of intermediate azaenolate 14 with an electrophile (equation 7) °. Analogous reactions with a chiral naphthaldehyde imine were also reported . 

Addition of amines to 1,2-dihydronaphthalene oxide has been claimed1 1 to yield product corresponding to attack at the epoxide carbon atom furthest from the benzene ring. The validity of this claim... 

Ring cleavage of 1,2-dihydronaphthalene oxideM<1 and 1.4-dihydronaphthalene oxide 1 has been carried out with hydrochloric acid and hydrobromio acid respectively. Though it is Bafe to suppose a trarw-Mohydrin to have been formed in the second case (Eq. 726). the product stereochemistry is somewhat in doubt in the first Eq. 726). 

It is interesting to note that the archival enthalpies of formation of 1,2- and 1,4-dihydronaphthalene differ by 12.7 2.3 kJ mol-1 and those of their 1-ring de-benzoated counterparts 1,3- and 1,4-cyclohexadiene have been suggested to be nearly identical (see Reference 8). 

The dihydronaphthalene in which the double bond is conjugated with the aromatic ring is more stable thus 1,2-dihydronaphthalene has a lower heat of hydrogenation than 1,4-dihydronaphthalene. 

Photoreaction of hexafluorobenzene (11) with cycloalkenes proceeds at only the ortho mode with exo selectivity (12 > 13) [85] (Scheme 8). The exo selectivity decreased with increasing the ring size of cycloalkenes. However, the photoreaction of 11 with indene or dihydronaphthalene predominates the endo adduct due to the ir-stacking. The ether 14 reacts regioselectivity and stereoselec-tively to produce 15-17 [86],... 

The anti -stereocontrolled alkylative ring-opening reaction of azabicyclic alkenes has been reported.100 iV-(2-Pyridyl)sulfonylazabenzonorbornadiene (36) has reacted with Grignard reagents in the presence of catalytic amounts of CuCN to afford, in good yields and excellent anti selectivity, the corresponding dihydronaphthalene-1-amines (37) (Scheme 20). 

Co-ozonolysis of 1,2-dihydronaphthalene with formaldehyde, acetyl cyanide (pyruvonitrile), benzoyl cyanide, or acetaldehyde afforded an ozonide attached to a benzaldehyde group 89 and none of the isomeric ozonide with a propionaldehyde group. This indicates the preference for scission of the molozonide so as to favor conjugation between the aromatic ring and the aldehyde group rather than with the carbonyl oxide group. Subsequent co-ozonolysis of products 89 with vinyl acetate produced diozonides 90, as shown in Scheme 26 and Table 11. 

This possibility of intimate association of rhodium with the aromatic ring suggests further experiments. A logical extension of asymmetric syntheses involving prochir-al reactants is a kinetic resolution with related chiral reactants under similar conditions. In the one case of hydroboration-amination where this has been applied, it has proved to be very effective. The reactant was prepared directly by a Heck reaction on 1,2-dihydronaphthalene, and under the standard conditions of catalytic hydrobora-tion gave >45% of both enantiomerically pure recovered alkene with (after oxidative work-up) the alcohol of opposite hand, mainly as the trans-isomer. This procedure forms a simple and potentially useful route to pharmacologically active substances, demonstrated by the racemic synthesis shown [105] (Scheme 34). 

Some of these values are very approximate, especially for the dihydronaphthalenes due to ring stain uncertainties in the radical, and are meant to serve only as a rough guide until more direct evidence is available. 

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