By Stevens rearrangement

At low temperatures cyclopropenones and enamines or ketene acetals were shown to yield 2-azonia-bicyclo(3,l, 0)hex-3-enolates-3 (371, X=0), which can be isomerized thermally to penta-2,4-diene amides(372, X=0). At elevated temperatures the amides were found to be the principal products arising from C-N-insertion 237) (insertion of the cyclopropenone three-carbon unit into the C-N bond of the enamine). These were accompanied in some cases by 3-aminoenones 373 arising from C-C-insertion 237) (insertion of the cyclopropenone into the C-C double bond of the enamine) and a-amino cyclopentenones 375 formed by Stevens rearrangement of the ylide 369 and cyclopentenones 374 ( condensation 237)). 

Intramolecular N-alkylation of tertiary amines, followed by Stevens rearrangement, enables rapid preparation of elaborate polycyclic structures [1235-1238]. Illustrative examples are given in Table 4.16. 

The related benzotriazocinones (317) are obtained by cyclization of dialkylhydrazones (316) and mild thermolysis of the quaternary hydrazones (73CPB2375). The latter undergo ring contraction to diazepines by Stevens rearrangement. 

The ochotensine-type base (173 X = H2) has been obtained by Stevens rearrangement of the non-phenolic AT-methyltetrahydroprotoberberinium salt (172) with methyl sulphinyl carbanion (Scheme 19). Details have appeared of the benzocyc-lobutenyl route to (173 X = CH2) (c/. Vol. 4). The mass-spectral fragmentation pattern of various fumariline type alkaloids has been studied. ... 

Scheme 5.5 First C—C bond formation by Stevens rearrangement (left) or oxonium ylide route ...

The Cu(acac)2-catalyzed decomposition of the diazo ketone 55 afforded the ring-expanded 5,7-fused benzazepine 57 via the initial formation of ammonium ylide 56 followed by Stevens rearrangement of the benzylic... 

The interest at that time was focused on the conformational aspects of the [3,3] metacyclophanes 1, or in their conversion to dihydropyrene 4 via methylation reactions followed by Stevens rearrangement and Hofmann elimination (Fig. 16.1). Also in later work, compounds analogous to 2 and 3 were observed as side products [3, 4]. 

Such reductive ring contractions of sulfones are formally similar to two other methods capable of supplanting a sulfur atom by a carbon-carbon double bond the Ramberg-Backlundand Stevens rearrangements. The distinguishing feature of this novel approach to cyclobutenes consists in the resultant higher level of alkyl substitution at the sp -hybridized centers. 

The aza-[2,3]-Wittig rearrangement of a vinylaziridine-derived quaternary azir-idinium ylide (i.e., [2,3]-Stevens rearrangement) has recently been reported (Scheme 2.53) [86], The aziridinium ylide 219, generated by the intramolecular reaction of a copper carbenoid tethered to a vinylaziridine, underwent a [2,3]-Ste-vens rearrangement to furnish the bicydic amine 220 with the indolizidine skeleton. 

Rearrangements closely resembling the Stevens rearrangement have been investigated by applying Grignard reagents or potassium t-butoxide in dimethyl-formamide (low availability of protons) to cis- and trans-2,4-diphenylthietane oxides and dioxides . The main results are summarized in equation 97 and 98. 

Kametani et al. (163-165) studied the Stevens rearrangement using sodium bis(2-methoxyethoxy)aluminum hydride as the base in dioxane. It became clear from studies using deuterium-labeled or optically active compounds that quasi-axially oriented hydrogens at C-8 and C-14 were independently abstracted by the base, leading to a spirobenzylisoquinoline and an 8-... 

When we allowed pentafluorophenyl-lithium to decompose in ether in the presence of an excess of N, ZV-dimethy laniline we obtained the compounds (92) 70, X = F), (94), the latter as the major compound, and a product which was shown to be (97). That this latter compound did not arise by metallation of 2V,lV-dimethylaniline followed by addition to tetrafluorobenzyne was shown by quenching the reaction mixture with deuterium oxide. No deuterium incorporation was detected. The compound (97) provides a rare example of a product derived by a Stevens rearrangement in which aryl migration has occurred b>. 

Muroni et al. have reported a tandem metallocarbenoid/ylide/[l,2]-Stevens rearrangement <2004TA2609>. The azoniaspirocycle ylide 5 is formed by trapping of the metallocarbene precursor (Equation 14). Heating the ylide in toluene then gave indolizidinone 55 as a single diastereoisomer. 

A hitherto unknown type of rearrangement of l-(l-alkynyl)cyclopropanols (321) to cyclopent-2-en-l-ones (322) mediated by octacarbonyldicobalt" and hexacarbonyldicobalt" complexes has been described. A possible pathway for the transformation is outlined in Scheme 101. A -proton transfer accompanied by a metal-mediated Stevens rearrangement, which converts a coordinated dimethylsulfane... 

Cleavage of a-aminoketones and their quaternary ammonium salts by sodium amalgam or zinc dust and acid has been used in synthetic procedures. This process was a key step in determining the stereochemistry of the Stevens rearrangement for... 

Racemic argemonine (5) has been synthesized from the readily available tetrahydro-6,12-methanodibenz[c,/Iazocine (74) (120-122) through a sequence involving a Stevens rearrangement and in an overall yield of 53% from 74 (Scheme 11) (123). Hofmann degradation of 74 furnished the cxo-methylene compound 75 (120,122). An oxidative ring expansion of 75 afforded ketone 76, which was then reduced to secondary alcohol 77. A transannular reaction, effected by acetic acid-acetic anhydride, resulted in the formation of the tetra-... 

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