Biomimetic α-acylimmonium cyclisations of unactivated olefin

Dijkink, J.; Speckamp, W. N.

doi:10.1016/s0040-4020(01)93599-9

Cited by 61 publications

(30 citation statements)

References 33 publications

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“…clearly indicates that all of them have the same configuration (endo) at C(11). Various authors have concluded that endo-configurated products are formed invariably in this type of cyclization [32] [33] and in one case a definite proof has been provided by X-ray crystallography ( [32], 'Note added in proof). The exclusive formation of products with endo-configuration in all cases reported so far, has been explained by invoking a chair transition state between an (E)-iminium ion (such as I1 and 111) and the reaction products [32] [33].…”

Section: Methodsmentioning

confidence: 99%

“…Various authors have concluded that endo-configurated products are formed invariably in this type of cyclization [32] [33] and in one case a definite proof has been provided by X-ray crystallography ( [32], 'Note added in proof). The exclusive formation of products with endo-configuration in all cases reported so far, has been explained by invoking a chair transition state between an (E)-iminium ion (such as I1 and 111) and the reaction products [32] [33]. In our case, the preference to adopt a chair transition state is expected to be even more pronounced because the (potential) products of a boat transition state would suffer from a 1,3-diaxial interaction between H3C(21) and H,C(lO).…”

Section: Methodsmentioning

confidence: 99%

“…57 (s, 3H). ',C-NMK (25 MHz): 178.7 (2s); 133.9 (s); 120.3 (d); 64.8 (s); 39.9 (d); 31.1 ( t ) ; 28.6 (21); 26.7 (t); 24.4 (t); 24.2 (9); 23.6 (4); 23.2 (4 [32]. To a cold solution of 23 (405 mg, 1.7 mmol) in 40 ml EtOH were added 151 mg (4 mmol) NaBH, (Fluka, purum).…”

Section: )mentioning

confidence: 99%

“…Many attempts to induce this reaction with a variety of Lewis and Bronsted acids led to intractable mixtures containing little, if any, 5, 6 or 7, and for this reason different approaches to the synthesis of aristoteline-type alkaloids were investigated. An efficient route to the 3-azabicyclo[3.3. llnonane skeleton has been described by Speckamp et al [32], who have reported that the ethoxylactam 19 (Scheme 5) cyclizes smoothly upon treatment with HCOOH to give a 9:l mixture of 20 and 21.…”

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confidence: 94%

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Synthesis of (−)‐Hobartine and Related Indole Alkaloids

Darbre

Nossbaumer

Borschberg

1984

Helvetica Chimica Acta

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SummaryAn improved method for obtaining optically pure (S)-( 1-p -menthen-8-yl)amine (12) has led to expedient syntheses of two hypothetical biogenetic intermediates on the way to aristoteline (7), namely (S)-N-(l-p-menthen-8-yl)-2-(3-indolyl)ethylamine (3) and (S)-N-(l-p-menthen-8-yl)-2-(3-indolyl)ethylideneamine (4). The latter has been transformed into (-)-hobarthe (6) in 64 % yield via a stereoselective biomimetic cyclization by treatment with HCOOH. This unambiguous synthesis establishes the hitherto unknown absolute configuration of (-)-hobartine (6). Several model cyclization reactions of N-substituted a -(terpen-%yl)imine derivatives yielding unsaturated 3-azabicyclo-[3.3. llnonane compounds are described. Aristoteline (7) was isolated in 1975 by Bick et al. [l] from the New Zealand plant Aristotelia serrata as the first member of a novel group of indole alkaloids. The same authors determined its pentacyclic structure by X-ray crystallography. Subsequently, this natural product was detected in other plants [2] [3] together with several related alkaloids'), of which two, the tetracyclic compounds makomakine (5) and hobartine (6) (Scheme I ) , are on the same oxidation level as aristoteline (7).The outstanding feature of this alkaloid family is that most of its members embody an intact monoterpene unit, whereas the vast majority of the known mevalonoid indole alkaloids originate from secologanin which arises from an oxidative cleavage of a preformed cyclopentane monoterpene. (cf. e.g. [ 141 and ref. therein). A plausible pathway to the aristoteline family has been proposed by Bick et al. [15] and, in a slightly modified version, by Hesse et al. [3]. Their proposal which is relevant to the present discussion is shown in Scheme I :According to Scheme I cyclization of nerylpyrophosphate (2) in the presence of tryptamine (1) leads to 3 as the first biogenetic intermediate containing all C-atoms of the aristoteline-type alkaloids. To date, this compound has not been detected in natural sources, but an oxidized version of its skeleton is present in frutico-') Presented in part at the 'Herbstversammlung

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: )mentioning

confidence: 99%

mentioning

confidence: 94%

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Synthesis of (−)‐Hobartine and Related Indole Alkaloids

Darbre

Nossbaumer

Borschberg

1984

Helvetica Chimica Acta

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“…Our reactiond esign combines a Mukaiyama-Manniche ventt os et the keyo xocarbenium intermediate II, [6,7] along with first use of at ertiary enamide functionality [5,8,9] as the central dipolara lkene. [10] Upon generating an N-acyliminium ion III, [11,12] which is efficiently trapped by an enoxysilane in the terminatings tep of the catalytic cycle( Scheme 1, d), [13,14] the tertiaryenamide acts as the expected 1,2-dipole. [9] This Mukaiyama-Mannich-Prins cascade transformation operates through an uncommon multi-step catalytic cycle which reveals sequentially two N-acyliminium I and III and one silyloxycarbenium II intermediates, providing us with an unusual hybrid Prins/aza-Prins [15][16][17][18] approach(Scheme1,c and d).…”

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confidence: 99%

Novel Hybrid Prins/Aza‐Prins Oxocarbenium/N‐Acyliminium Cascade: Expedient Access to Complex Indolizidines

Berthet

Beauseigneur

Moine

et al. 2018

Chemistry A European J

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Heavy silyl enol ethers (mostly TIPS and TBS) combine with cyclic N-alkenyl N-acyliminium salts generated in situ from their N,O-acetal precursors, to furnish highly functionalized indolizidines through an unprecedented double Mukaiyama-Mannich-Prins cascade transformation. This novel cascade annulation process demonstrates a promising scope, and takes place mostly catalytically with interesting stereocontrol. Furthermore, an appealing facet of this chemistry is emphasized with a bicatalytic approach by which the Mannich-Prins cascade follows a Ru-catalyzed N-allylamide to N-(E)-propenyl isomerization of the aminal counterpart in a one-pot operation.

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