TY - JOUR
T1 - Synthesis and highly selective Diels-Alder cycloadditions of the new dienes N-substituted 2,3,5,6-tetrahydrobenzoxazol-2-ones
AU - Martínez, Rafael
AU - Jiménez-Vázquez, Hugo A.
AU - Delgado, Francisco
AU - Tamariz, Joaquín
N1 - Funding Information:
We thank Fernando Labarrios for his help in spectrometric measurements. J. T. is grateful to CGPI/IPN (Grants 916510, 200410, 32.14, and 200140) and CONACYT (Grants 1203-E9203 and 32273-E) for financial support. R. M. thanks CGPI/IPN and PIFI/IPN for scholarships, and Ludwig K. Hellweg Foundation for a scholarship complement. H. A. J. acknowledges support from CONACYT (Grant 3251P), and thanks IPN's Programa de Contratación de Personal de Excelencia.
PY - 2003/1/20
Y1 - 2003/1/20
N2 - The synthesis of the new dienes N-substituted 2,3,4,5-tetrahydrobenzoxazol-2-ones 8a-8c is described, through a one-step convergent process from 1,2-cyclohexanedione (7a) and the corresponding isocyanates 2a-2c. The presence of electron-donor substituents in the aryl ring of the isocyanate gave rise to the exclusive formation of the captodative olefins 10. Diene 8a proved to be reactive and stereoselective in Diels-Alder additions with a cyclic olefin. The reaction with acetylenic dienophiles yielded the 2,3-dihydrobenzoxazol-2-ones 21 and 24, as the products of sequential [4+2] cycloaddition and retro-Diels-Alder reactions. Methyl vinyl ketone (22) underwent regio- and stereoselective tandem Diels-Alder and Michael additions to give propellane 29a. Evidence of an endo π-pyramidalization of the central double bond of adduct 19 would rationalize the exo stereoselection in the formation of 29a. The regioselectivity in these reactions has been rationalized in terms of FMO theory by ab initio calculations.
AB - The synthesis of the new dienes N-substituted 2,3,4,5-tetrahydrobenzoxazol-2-ones 8a-8c is described, through a one-step convergent process from 1,2-cyclohexanedione (7a) and the corresponding isocyanates 2a-2c. The presence of electron-donor substituents in the aryl ring of the isocyanate gave rise to the exclusive formation of the captodative olefins 10. Diene 8a proved to be reactive and stereoselective in Diels-Alder additions with a cyclic olefin. The reaction with acetylenic dienophiles yielded the 2,3-dihydrobenzoxazol-2-ones 21 and 24, as the products of sequential [4+2] cycloaddition and retro-Diels-Alder reactions. Methyl vinyl ketone (22) underwent regio- and stereoselective tandem Diels-Alder and Michael additions to give propellane 29a. Evidence of an endo π-pyramidalization of the central double bond of adduct 19 would rationalize the exo stereoselection in the formation of 29a. The regioselectivity in these reactions has been rationalized in terms of FMO theory by ab initio calculations.
KW - Diels-Alder
KW - Dienes
KW - Michael addition
KW - Propellanes
KW - Tetrahydrobenzoxazol-2-ones
KW - π-pyramidalization
UR - http://www.scopus.com/inward/record.url?scp=0037454658&partnerID=8YFLogxK
U2 - 10.1016/S0040-4020(02)01536-3
DO - 10.1016/S0040-4020(02)01536-3
M3 - Artículo
SN - 0040-4020
VL - 59
SP - 481
EP - 492
JO - Tetrahedron
JF - Tetrahedron
IS - 4
ER -