Synthesis of the tricyclic core of sarain A. Use of formaldehyde in an intramolecular Grigg azomethine ylide cyclization

Journal of Organic Chemistry

Volumn 63, Issue 26, 1998, Pages 9616-9617

  Denhart, Derek J ^a   Griffith, David A ^a   Heathcock, Clayton H ^a  

^a UNIVERSITY OF CALIFORNIA   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

ALKALOID; AZO COMPOUND; FORMALDEHYDE; METHYL GROUP; NATURAL PRODUCT;

ALKYLATION; ARTICLE; CYCLIZATION; DIASTEREOISOMER; ENANTIOMER; MOLECULAR INTERACTION; MOLECULAR MODEL; OXIDATION; REACTION ANALYSIS; SPONGE (PORIFERA); SYNTHESIS;

EID: 0032567447     PISSN: 00223263     EISSN: None     Source Type: Journal    
DOI: 10.1021/jo981801b     Document Type: Article

References (19)

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17. Our route diverges from the Weinreb route in the way that bicyclic lactam 17 is transformed into the tricyclic structure of 23. In our approach, the six-membered lactam ring is opened by a sort of Dieckman reaction to give the/3 keto ester 19. After modification of the functionality, the original six-membered ring is reformed by Michael addition of the pendant aminoethyl group, giving 23. In the Weinreb approach, construction of the tricyclic system is accomplished directly by addition of a pendant allylsilane to an immonium ion, derived by partial reduction of the lactam carbonyl. In early work we did explore a similar strategy using an aldehyde and the corresponding dioxolane in place of the allylsilane. However, as has been described in ref 5, these attempts failed. It should be noted that the modified approach reported here, although more complicated, is not significantly less efficient-requiring only five steps to convert 18 into ester 23.
18. However, in recently completed work, the Weinreb group have succeeded in introducing a one-carbon unit at Cl: Irie, O.; Henry, J.; Samizu, K.; Weinreb, S. M. J. Org. Chem., in press.
19. This anticipation has now been confirmed by Weinreb and coworkers; ref 13.