Oxa-Pictet-Spengler

The oxa-Pictet-Spengler reaction has been used with success to prepare dihydrofurano[2,3-c]pyrans and isochromans from l-(3-furyl)alkan-2-ols and 2-(3 ,4 -dihydroxy)phenylethanol, respectively. Furanyl alcohol 32 reacted with isobutyraldehyde 33 in the presence of p-toluenesulfonic acid to give the corresponding CI5-5,7-diisopropyl 4,5-dihydro-7H-furano[2,3-c]pyran 34 in good yield. ... 

For that reason an intramolecular benzannulation was developed, which incorporates all components for the intramolecular alkoxycarbonylation into the naphthoquinone 105 [65]. Based on that strategy a short and convergent pathway for the synthesis of racemic deoxyfrenolicin 108 was accomplished. Xu et al. replaced the allylacetylene 100 in the reaction sequence for nanaomycin A by alkynoate 106. The benzannulation product 107 was an appropriate precursor for a subsequent tandem oxa-Pictet-Spengler cyclisation/DDQ-induced coupling reaction [66]. Following this strategy the total synthesis of enan-tiomerically pure deoxyfrenolicin could be accomplished (Scheme 48). 

Excellent yields of isochromans are obtained when 2-phenylethanol derivatives react with aldehydes and, with lower yields, ketones in the presence of the zeolite Ersorb-4a. This variation of the oxa-Pictet-Spengler reaction is simple, cheap and environmentally-ffiendly <060BC1220>. 

When dioxolanes bearing a suitably positioned electron-rich aryl group are treated with TiCU, they can undergo an oxa Pictet-Spengler rearrangement as illustrated by the conversion of 102 into 103 (Equation 12) <2004TL411, 2005AJC565>. 

Synthesis of isochromanes and related pyran-type heterocycles using oxa-Pictet-Spengler cyclization 06S187. 

The oxa-Pictet-Spengler reaction, an intramolecular cyclization, is an important method for the synthesis of phthalans. It requires strong Brpnsted acid and the... 

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