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On the Scope of a Prins ‐Type Cyclization of Oxonium Ions
Author(s) -
Fráter Georg,
Müller Urs,
Kraft Philip
Publication year - 2004
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.200490248
Subject(s) - oxonium ion , chemistry , tetrahydrofuran , carboxylate , prins reaction , stereochemistry , aldehyde , ketene , medicinal chemistry , ion , organic chemistry , catalysis , solvent
Abstract The Prins cyclization of an aldehyde 1 with a homoallylic alcohol 2 , affording tetrahydro‐2 H ‐pyrans 4 via the oxonium ion 3 as central intermediate, was conceptually transferred to (alk‐3‐enyloxy)acrylates 6 , which form a related oxonium ion 7 upon treatment with acids ( Scheme 1 ). The scope and utility of this modification of the Prins ‐type cyclization of oxonium ions is discussed exemplarily by means of the syntheses of ten tetrahydro‐2 H ‐pyran and tetrahydrofuran derivatives, featuring diverse substitution patterns as well as different degrees of molecular complexity. These target structures include (±)‐ethyl (2 RS )‐2‐[(2 RS ,4 SR ,6 RS )‐ and (2 SR ,4 RS ,6 SR )‐2‐tetahydro‐4‐hydroxy‐6‐methylpyran‐2‐yl]propanoate ( 23 ), (±)‐ethyl [(2 RS , 3 RS )‐tetrahydro‐3‐isopropenylfuran‐2‐yl]acetate ( 32 ), (±)‐ethyl (2 Z )‐3‐(tetrahydro‐2,2‐dimethylfuran‐3‐yl)acrylate ( 37 ), (±)‐(3a RS ,6 RS , 7a RS )‐octahydro‐7a‐methylbenzofuran‐6‐yl formate ( 42 ), (±)‐ethyl (2 RS ,3 RS ,4a RS ,8 SR ,8a RS )‐hexahydro‐2,5,5,8‐tetramethyl‐7‐oxo‐2 H ,5 H ‐pyrano[4,3‐ b ]pyran‐3‐carboxylate ( 48 ), and (±)‐ethyl (2 RS ,3 RS ,6 SR )‐tetrahydro‐6‐(2‐methoxy‐2‐oxoethyl)‐3‐methyl‐2 H ‐pyran‐2‐carboxylate ( 53 ) (see Schemes 3 and 5–8 ). Besides the stereochemistry and mechanistic details of this versatile oxonium‐ion cyclization, the synthesis of suitable starting materials is also described.