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Title: Origins of Endo Selectivity in Diels–Alder Reactions of Cyclic Allene Dienophiles
Abstract

Strained cyclic allenes, first discovered in 1966 by Wittig and co‐workers, have recently emerged as valuable synthetic building blocks. Previous experimental investigations, and computations reported here, demonstrate that the Diels–Alder reactions of furans and pyrroles with 1,2‐cyclohexadiene and oxa‐ and azaheterocyclic analogs proceed withendoselectivity. Thisendoselectivity gives the adduct with the allylic saturated carbon of the cyclic alleneendoto the diene carbons. The selectivity is very general and useful in synthetic applications. Our computational study establishes the origins of thisendoselectivity. We analyze the helical frontier molecular orbitals of strained cyclic allenes and show how secondary orbital and electrostatic effects influence stereoselectivity. The LUMO of carbon‐3 of the allene (C‐3 is not involved in primary orbital interactions) interacts in a stabilizing fashion with the HOMO of the diene in such a way that the carbon of the cyclic allene attached to C‐1 favors theendoposition in the transition state. The furan LUMO, allene HOMO interaction reinforces this preference. These mechanistic studies are expected to prompt the further use of long‐avoided strained cyclic allenes in chemical synthesis.

 
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NSF-PAR ID:
10232273
Author(s) / Creator(s):
 ;  ;  ;  ;  
Publisher / Repository:
Wiley Blackwell (John Wiley & Sons)
Date Published:
Journal Name:
Angewandte Chemie International Edition
Volume:
60
Issue:
27
ISSN:
1433-7851
Format(s):
Medium: X Size: p. 14989-14997
Size(s):
["p. 14989-14997"]
Sponsoring Org:
National Science Foundation
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