Six-Membered Cyclic Nitronates as 1,3-Dipoles in Formal [3 + 3]-Cycloaddition with Donor–Acceptor Cyclopropanes. Synthesis of New Type of Bicyclic Nitrosoacetals

Abstract

The first formal [3 + 3]-cycloaddition of nitronates with donor-acceptor cyclopropanes is reported. The reaction is catalyzed by ytterbium trifluoromethanesulfonate and leads to hitherto unknown bicyclic nitrosoacetals, possessing two annelated six-membered rings.

Formal [3+3]-cycloaddition of 3-methyl-5,6-dihydro-4H-1,2-oxazine-N-oxides with cyclopropane dicarboxylates under hyperbaric conditions

“…Previously we have observed the equilibrium 4-A 4-B for bridge-head unsubstituted (R 2 = H) nitrosoacetals 4. 4 However, now we were unable see corresponding EXSY-peaks, which may be evident of a higher inversion barrier. 16 Additionally, in the case of 4ab, where the minor conformation is relatively high (4-A/4-B = 3:1), NOESY-interactions were intense enough to reveal its configuration (see supporting information for details).…”

“…Less active DACs 1 (R 1 = H, n-Pr) failed to react, as previously observed for reactions with 3-H substituted nitronates. 4 All adducts 4 exhibit two sets of signals in NMR spectra, that we attribute to two possible conformations 4-A and 4-B ( Figure 2). Previously we have observed the equilibrium 4-A 4-B for bridge-head unsubstituted (R 2 = H) nitrosoacetals 4.…”

“…2 Recently, we have described formal [3+3]-cycloaddition reactions of DAC 1 with acyclic silyl nitronates 2 3 and some cyclic nitronates (5,6-dihydro-4H-1,2-oxazine-N-oxides 3, Scheme 1). 4 However, while 3-unsubstituted nitronates 3 (R 1 = H) gave the corresponding adducts in good yields, their substituted analogue (R 1 = Me) failed to react. Herein, we describe an approach for overcoming this difficulty.…”

Novel Formal [3+3] Cycloaddition of Silyl Nitronates with Activated Cyclo­propanes and Its Application in the Synthesis of Pyrroline-N-oxides

“…[7][8][9] Since the initial report of Kerr and coworkers who described nitrone cycloaddition (Scheme 2, eq. 1), 7 these transformations have been widely investigated.…”

Synthesis of Saturated Heterocycles via Metal-Catalyzed Formal Cycloaddition Reactions That Generate a C–N or C–O Bond

“…[99] Interesting further extensions of the methodology include the use of cobalt complexes of alkynyl cyclopropanes diesters as a new approach for donor-acceptor activation of the three-membered ring, [100] the use of nitrones derived from isatin to obtain important spiroxindole products, [101] and the use of cyclic nitrones as substrates. [102] Scheme 7.14: Formal [3+3] cycloadditions of cyclopropanes with nitrones and applications in the total synthesis of natural alkaloids.…”