Cycloaddition 1-naphthyl moieties

The introduction of a bulky, optically active amino function at C-2 of 4-phenyl-l-thiabutadiene and activation by the addition of AcCl prior to cycloaddition with Wphenylmaleimide, known to exhibit a high endo preference, results in the formation of two diastereomers. However, the exo product is the major component and indeed this diastereo-mer is the sole adduct when cyclopentene is used as the dienophile. Calculations point to a preference for exo addition from the same face of the molecule as the naphthyl moiety and this is supported by the observed R stereochemistry at the three chiral centers in the cyclopenta[A]dihydrothiopyran 434 (Scheme 140) <1996TL123>. 

Intramolecular Photocycloaddition of N—P4—A. Although the photocycloaddition of anthracene [85-100] and that of naphthalene [65-67,80-82] have been extensively studied, until recently relatively little has been reported on the cross-photocycloaddition between an anthracene and a naphthalene moiety [101-110], The main reason for this is the large difference in the quantum yields between the photocycloaddition of anthracene and the cross-photocycloaddition of anthracene and naphthalene. Thus, bichromophoric molecules with anthryl as one chromophore and naphthyl as the other generally undergo intermolecular an-thryl-anthryl cycloaddition rather than intramolecular cross-cycloaddition when irradiated. 

Larock and coworkers uncovered a facile synthesis of dihydrobenzisoxazoles by the insertion of arynes into C-O o-bond of oxaziridines. Notably, in this reaction, the bulky tertiary butyl group present on oxaziridine moiety was the key to success for the generation of dihydrobenzisoxazoles 75 with high yields (Scheme 32) [55]. This reaction was carried out in the presence of CsF, in DME at 90 °C with stoichiometric amounts of Na2C03. Mechanistically, the reaction can be considered in two ways. In pathway a, the nitrones intermediate 74 generated from 73 xmdergoes an efficient [3+2] cycloaddition reaction to afford 75. Alternatively, the insertion of arynes into the C-O o-bond of oxaziridines 73 can also furnish the desired product (pathway b). It is noteworthy that this reaction can lead to (hetero) aryl-, alkyl-, and naphthyl-substituted dihydrobenzisoxazoles. 

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