Stereochemistry of the Cycloaddition of 1,3‐Diphenyl‐2‐azaallyllithium to Alkenes at 0 °C

Abstract

munication on a total synthesis16] we now publish our results on a biogenetically oriented indole-camptothecin rearrangement.Using the easily accessible indolic compound (3)"l as starting material, the indole-quinoline conversion could be carried out in two simple steps.

Additions and cycloadditions of 2-phenylallylmagnesium phenoxide to carbon-carbon double bonds

“…Reaction of phenanthrene with 1 HMPA gave the 9,10dehydro 1:1 adduct 10. Since 10 must be formed by dehydrogenation of the corresponding 9,10-dihydrophenanthrene (11), and atmospheric oxygen is known to convert dihydrophenanthrenes to phenanthrenes,11 we attempted but failed to isolate the initial adduct 11 by carrying out all experimental operations under nitrogen. Since unsubstituted 9,10-dihydrophenanthrene also was detected in the reaction mixture, 11 may have produced 10 by hydrogen transfer to phenanthrene.…”

“…The former was isolated by GLC on column A at 290 °C, but the latter decomposed during attempted isolation. The compound with m/e 298 was identified as r-l,i-2,e-4-triphenylcyclopentane (2) by its 220-MHz NMR spectrum:8 IR (C2C14) 3100 (m), 3080 (m), 3040 (s), 2950 (m), 1600 (s), 1500 (s), 1450 (s), 1060 (m); mass spectrum m/e (rel intensity) 298 (55), 207 (11), 194 (54), 193 (100), 180 (11), 179 (27), 178 (23), 168 (20) , 165 (43).…”

“…5 The adducts of 2-azaallyllithium with trans-and as-stilbene appear to be those predicted by conservation of orbital symmetry. 11 Two structural features which promote anionic [3 + 2] cycloaddition are electron-withdrawing substituents on the carboncarbon double bond and stabilization of charge in the cyclopentyl anion by a nitrogen atom (in the form of a pyrrolidine anion), or a carbonyl, cyano, or aryl substituent.…”

Cycloadditions of Nonstabilized2-Azaallyllithiums (2-Azaallyl Anions) and Azomethine Ylides withAlkenes: [3+2] Approaches to Pyrrolidinesand Application to Alkaloid Total Synthesis

“…45, 46 Tsuge, Kanemasa, and co-workers reported the first example of a nonstereospecific cycloaddition of a semistabilized 2-azaallyl anion with Z-stilbene, clearly indicative of a stepwise pathway (see 9 → 11 in Scheme 3 above). 45, 46 Tsuge, Kanemasa, and co-workers reported the first example of a nonstereospecific cycloaddition of a semistabilized 2-azaallyl anion with Z-stilbene, clearly indicative of a stepwise pathway (see 9 → 11 in Scheme 3 above).…”

Cycloadditions of Nonstabilized 2‐Azaallyllithiums (2‐Azaallyl Anions) and Azomethine Ylides with Alkenes: [3 + 2] Approaches to Pyrrolidines and Application to Alkaloid Total Synthesis.

“…Kauffmann proposed in 1972 that the cycloadditions of 1,3-diphenyl-2-azaallyllithium with E-and Z-stilbene were concerted processes based on their stereospecificity (Scheme 19), but recognized that a stepwise intermediate analogous to 78 might be involved as long as bond rotations were slow relative to ring closure. 45,46 Tsuge, Kanemasa, and co-workers reported the first example of a nonstereospecific cycloaddition of a semistabilized 2-azaallyl anion with Z-stilbene, clearly indicative of a stepwise pathway (see 9 → 11 in Scheme 3 above). 5 We have found that most of the cycloadditions of nonstabilized 2azaallyllithiums proceed with retention of the anionophile geometry, but we have found a few examples of non-stereospecific additions, again involving Z-stilbene (e.g.…”