Carbon-carbon alkylation of enamines with mannich bases II. A new synthesis of pyran containing fused ring systems.

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

“…Strandtmann and his research group reported a new strategy to produce 3-morpholino-2,2-dimethyl-2,3-dihydro-1H-naphtho[2,1-b]pyran (62) from 2-naphthol Mannich bases (63) and an enamine (Scheme 25; yield not reported) [49,50]. The proposed mechanism involved elimination of the dimethylamine from the Mannich base followed by a Michael-type addition to the enamine.…”

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

“…Formaldehyde (a non-enolizable aldehyde) is known to give facile reaction with 2-naphthol to produce Mannich bases (2) in the presence of secondary amines. [30][31][32] This evidence of retro-aldol disproportionation led to a reassessment of the mechanism for the formation of compounds 1 as shown in Scheme 3. A report by Strandtmann et al 32 described the formation of 2,2-dialkyl-3-dialkylamino-2,3-dihydro-1H-naphtho[2,1-b]pyrans from 2-naphthol Mannich bases and enamines via deamination followed by cycloaddition.…”

“…[30][31][32] This evidence of retro-aldol disproportionation led to a reassessment of the mechanism for the formation of compounds 1 as shown in Scheme 3. A report by Strandtmann et al 32 described the formation of 2,2-dialkyl-3-dialkylamino-2,3-dihydro-1H-naphtho[2,1-b]pyrans from 2-naphthol Mannich bases and enamines via deamination followed by cycloaddition. Based on this report, it became apparent that the retro-aldol breakdown products of 2,2-disubstituted-3-hydroxypropanals, namely, formaldehyde and 2,2-disubstituted acetaldehydes, met different fates resulting in facile formation of 2-naphthol Mannich bases and enamines, respectively.…”

“…[32][33][34] One involved reaction of 2-naphthol Mannich bases and enamines to pro- 32,33 The second one reported a simple method of preparing 2,2-dialkyl-3-dialkylaminonaphtho[2,1-b]pyran-1-ols from 2-hydroxy-1-naphthaldehyde and enamines. 34 We herein report a novel microwave-assisted synthesis of 2,…”

An unusual coupling of cyclohexenone cyclic ketals

“…The formation of symmetrical bisphenoxylakanes was shown to be general in that cyclic ketals 2 and 3 reacted under the same conditions to yield 1,3-diphenoxypropane (5) and 1,4-diphenoxybutane (6), respectively, spectral properties of which are given in Table I. A possible coupling mechanism (Scheme I) involves opening of the cyclic acetal4 5to yield diene 10, followed by bromination, and dehydrobomination to give 2phenoxyethanol (7).…”