Cycloisomerization of 1,6‐Dienes Mediated by Lewis Super Acids without Additives: Easy Access to Polysubstituted Six‐Membered Carbocycles

Abstract

The tin salt Sn(NTf2)4 (Tf=trifluoromethanesulfonyl) is an efficient catalyst for the selective and ring‐size‐specific cycloisomerization of highly substituted 1,6‐dienes to give six‐membered‐ring carbocycles (see scheme; X=C(CO2Et)2, C(CO2Me)2 C(CN)(CO2Et), etc.). This is the first Lewis acid catalyzed cycloisomerization of this type of substrate.

Access to Polycyclic Derivatives by Triflate‐Catalyzed Intramolecular Hydroarylation

“…The formation of lactones 3j-3l results from the Lewis acid catalysed reaction between the olefin and one of the ester groups. This dealkylative lactonisation process has already been observed for other examples, [25] and high selectivity was observed for the lactonisation of 4-methylpentenoates via alkyloxonium intermediates, which were observable by NMR spectroscopy. [26] In contrast with the results for 1j-1l, the analogous olefin 1m underwent carbocyclisation to form the fused six-membered ring 2m in yields of 53 and 35 % with the Bi III and In III catalysts, respectively (Table 4, Entry 4).…”

New Aldehydes by Catalytic Diene Cycloisomerisations

“…[9] More detailed data: 1 H NMR (CDCl 3 , 500 MHz): δ = 2.10 (2-H eq ), 1.93 (2-H ax ), 1.94 (3-H ax ), 1.34 (5-H eq ), 1.36 (5-H ax ), 2.17 (6-H eq ), 1.86 (6-H ax ), 1.22 (CH 3 CH 2 O 2 C eq ), 4.14 (CH 3 CH 2 O 2 C eq ), 1. …”

“…Furthermore, under the same conditions, the diprenyl cyanoacetate 2a produces the corresponding cyclohexene derivative 2b as a single diastereoisomer in 56 % isolated yield, as illustrated in Scheme 1. [9] Scheme 1.…”

Stereoselectivity of Metal-Catalyzed Cyclizations of 1,6-Dienes

“…35 However, it is difficult to explain the diastereoselectivity observed for compounds 49-53. Hence, each was obtained as a single diastereomer except for 52.…”