A stepwise mechanism for the formation of 2.pi. + 4.pi. cycloadducts in the ionic Diels-Alder reaction

Abstract

substitution, acid catalyst, and temperature. This is particularly useful in the case of the bicyclo[5.4.0]undecanes, which are not readily available.14 Supplementary Material Available: Spectral and other analytical data for 2, 6-10, and 12-16 and crystallographic experimental details, ortep drawings, and tables of positional and thermal parameters and significant distances and angles for 9 and 10 (20 pages). Ordering information is given on any current masthead page.(14) For previous syntheses of the bicyclo[5.4.0]undecane skeleton via intramolecular Diels-Alder reactions, see:

Bouncing off walls – widths of exit channels from shallow minima can dominate selectivity control

“…Reactions between butadienes and allyl cations have been studied extensively from both mechanistic and synthetic perspectives. Reactions of these two types of components can lead to 4-, 5-, 6-or 7-membered rings via concerted or stepwise (formal) (2 + 2)/[ p 2 + p 2], 1,2 (2 + 3)/[ p 2 + p 2], 3,4 (4 + 2)/[ p 4 + p 2] [5][6][7][8][9] (the so-called "ionic Diels-Alder reaction") or (4 + 3)/[ p 4 + p 2] 3,4,10-12 cycloaddition reactions, respectively (Scheme 1). Which products are observed can be inuenced by which substituents are attached to each component and the environment in which the reaction is run.…”

Absolute configuration of (1S,3R,8R)-10-bromomethyl-2,2-dichloro-3,7,7-trimethyltricyclo[6.4.0.01,3]dodec-9-ene

“…1. As observed in related compounds (Gassman & Gorman, 1990;Lassaba et al, 1997;Benharref et al, 2010), each molecule is built up from two fused six-and seven-membered rings. The sixmembered ring has roughly half-chair conformation with the puckering parameters: Q = 0.493 3 17, (Flack, 1983;Flack & Bernardinelli, 2000) and by the refinement of the Hooft's parameter, -0.021 (11) (Spek, 2009).…”

“…For biological properties of cyclopropane-containing products, see: Ajay Kumar et al (2012); Sow et al (2007); Symon et al (2005). For related structures, see: Benharref et al (2010); Gassman & Gorman (1990); Lassaba et al (1997). For conformations of rings, see: Cremer & Pople (1975); Boessenkool & Boyens (1980); For absolute structure, see: Flack (1983); Flack & Bernardinelli (2000); Spek (2009).…”

Dienolates of Cycloalkenones and α,β‐Unsaturated Esters Form Diels–Alder Adducts by a Michael/Michael‐Tandem Reaction Rather Than in One Step

“…[22] Allyl cations can undergo "cationic Diels-Alder reactions" with certain 1,3-dienes. [23] At least for 1,1,3-triarylallyl cations a 2-step course is plausible. [23a] This implies the formation of a carbenium-ion as an intermediate.…”