Englbert Bäuml

Concerted [4+2] and stepwise [2+2]cycloadditions of the triphenylallenyl cation with cyclopentadiene

Abstract The triphenylallenyl cation ( 5 ), generated in situ under different conditions, reacts with cyclopentadiene via allyl cations 7 and 9 . The exclusive formation of 7 from 12 and FSO3H proves a concerted [4+2]cycloaddition leading to 9 and suggests a stepwise [2+2]cycloaddition reaction to give 7 .

Synthesis of γ-lactones from alkenes employing p-methoxybenzyl chloride as +CH2CO−2 equivalent☆

The ZnCl2 catalyzed reaction of p-methoxybenzyl chloride with alkenes yields the 1:1 addition products 3, which are converted into the γ-lactones 4 via Ru(VIII) catalyzed oxidative degradation of the aromatic ring.

Synthesis of 1,1,2,2,3,3-hexamethyl-4,5-bis(methylene)cyclopentane

An efficient synthesis of the title compound 14 is reported, which employs the ZnCl2/Et2O catalyzed addition of acetyl chloride (4) to 2-methyl-2-butene (5) and the [3+ + 2] cycloaddition of the 1,1,2,3-tetramethylallyl cation to 2,3-dimethyl-2-butene as key steps.

[2+2]-cycloadditions of alkenes with the triphenylallenyl cation

The triphenylallenyl cation (8), generated from triphenylpropynol (7) and FSO3H, reacts with alkenes to give the allyl cations 12, which may be deprotonated to yield the methyleneccylobutenes 14. Alternatively, 12 can be converted into the 2-vinyl-indenes 13 via two subsequent electrocyclic reactions.

A carbocationic 1,3-alkenyl shift

Abstract The Lewis acid catalyzed rearrangement 7 → 13 is explained by a carbocationic 1,3-alkenyl shift via the cyclobutylcarbinyl cation 10 .

Prenyaticn of camphene - a carbocationic route to isosantalene and its derivatives

Abstract Camphene 1 is converted Into 8-chloromethylcamphene 3 via Prins reaction. Treatment of 3 with zinc chloride/ether In the presence of isobutene gives the 1:1 adduct 11, from which isosantalene 7, its isomer 6, and the corresponding alcohol 5 are obtained.