Synthesis of isochroman-3-ylacetates and isochromane-γ-lactones through rearrangement of aryldioxolanylacetates

Palladium/Imadazolium Salt Mediated Cyclisations for the Synthesis of Heterocyclic Compounds

“…When the phenyl substituted precursor 3.3 was subjected to the same reaction conditions, however, two isomeric products were isolated [18]. Benzylisochromene 4.3 [19], and benzylideneisochroman 4.4 [20] [21], nuclei were obtained in yields of 22% and 63% respectively, (Scheme 4). Isolation of benzylideneisochroman 4.4 as the major product in this case means the reaction probably proceeded via 6-exo cyclisation.…”

Synthesis of Oxacycles Employing the Oxa‐Pictet–Spengler Reaction: Recent Developments and New Prospects

“…Computational efforts [107] made on the intermediate oxocarbenium ions derived from 105 and 112 [115] to explain the stereochemical outcome of the reaction evidenced that the geometry and distance of the Z* intermediate which lead to the anti product, are predefined for a favourable eventual ring-forming reaction (Scheme 16). The E* isomer appears to be more stable because it can relieve much of the crowding necessitated by Z*.…”

The Oxa-Pictet-Spengler Cyclization: Synthesis of Isochromans and Related Pyran-Type Heterocycles

“…In a further extension of this process, the authors also demonstrated the conversion of methyl 4,5-trans-4-aryldioxolan-5-yl acetates into methylisochroman-3-yl acetates and the corresponding isochroman-g-lactones, a structural feature of the pyranonaphthoquinone antibiotics. 97 In a systematic exploration, Kaufman's group more recently demonstrated that the oxa-Pictet-Spengler isomerization of acetals 174, derived from threo-diols 175, stereoselectively gives 1,3-cis-disubstituted isochromans 176 when the substituents are bulkier or more complex than simple methyl groups (Table 3). 93 The rearrangement occurs under the promotion of TiCl 4 , with other Lewis acids such as BF 3 •Et 2 O being ineffective; however, in some isolated cases, this transformation was demonstrated to take place under p-toluenesulfonic acid assistance.…”