A Convenient One-Pot Synthesis of 2,2-Dialkyl-2,3-dihydro-1H-naphtho[2,1-b]pyrans

Abstract

This work describes a convenient one-pot procedure for the synthesis of 2,2-disubstituted 2,3-dihydro-1H-naphtho[2,1b]pyrans {i.e. 2,2-disubstituted 1H-benzo[f]chromans} by the reaction of 2-tetralones and a,a-disubstituted b-hydroxy propionaldehydes under acidic conditions.

Synthetic approaches to 3H‐naphtho[2,1‐b]pyrans and 2,3‐dihydro‐1H‐naphtho[2,1‐b]pyrans

“…Our efforts have also led to synthesis of three kinds of 2,3-dihydro-1H-naphtho [2,1-b]pyrans [56][57][58]. Reaction between 2-tetralone and substituted ortho-hydroxy aromatic aldehydes under acidic conditions resulted in formation of benzene-fused 2,3-dihydro-1H-naphtho[2,1-b]pyrans or 12H-benzo[a]xanthenes (67, Scheme 27) in moderate to excellent yields (55-94%) [56].…”

“…This study was later expanded to expeditiously and conviniently prepare 2,2,-dialkyl-2,3-dihydro-1H-naphtho[2,1-b]pyrans (68, Scheme 28) in 51-96% yeild range from 2-tetralone analogs and 2,2-dialkyl-3- hydroxy propanaldehydes (69) under anhydrous acidic conditions [57].…”

“…The most plausible mechanism involves the formation of aldol product (70) between the active methylene of 2-tetralone and the corresponding aldehyde. Subsequently, cyclization via nucleophilic attack leading to formation of the hemiacetal intermediate (71) followed by double dehydration (72) and aromatization by proton rearrangement produces stable products (68, Scheme 29) [57].…”

Aza-Diels–Alder reaction between N-aryl-1-oxo-1H-isoindolium ions and tert-enamides: Steric effects on reaction outcome

“…As mentioned earlier, N -aryl-1-oxo-1 H -isoindolium ions ( A , Scheme 1 ) undergo [4 + 2] imino-Diels–Alder cyclization with electron-rich alkenes [ 11 – 17 ], the steric effects on the outcome of these reactions has not been studied. In continuation of our efforts on the development of novel synthetic methodologies [ 27 – 36 ], we report herein a systematic study of steric and electronic effects of aryl substituents leading to substituted 6,6a-dihydroisoindolo[2,1- a ]quinolin-11(5 H )-ones (series 1 and 2) from 1-oxo-2-aryl-1 H -isoindolium ions ( A ) and appropriate tert -enamides ( Scheme 1 ). Although this is the first report of the use of tert -enamides as a dienophile for the hetero-Diels–Alder reaction with N -acyliminium cations, formation of isoindoloquinolines (series 1 and 2) was rather expected based on literature reports [ 11 – 17 ].…”

Novel synthesis of 2,2-dialkyl-3-dialkylamino-2,3-dihydro-1H-naphtho[2,1-b]pyrans

“…In pursuit of molecules with novel carbon skeletons making use of 2-tetralone and 2-naphthol analogs, [26][27][28][29][30][31] our research group has also developed novel procedures for the one-pot syntheses of 12H-benzo[a]xanthenes 26 and 2,2-dialkyl-2,3-dihydro-1H-naphtho[2,1-b]pyrans 27 from substituted ortho-hydroxy aromatic aldehydes and 2,2-dialkyl-3-hydroxypropanals, respectively, with 2-tetralone analogs under acidic conditions with high yields.…”