Ring-enlargement of Methoxynaphthalenes with Dichlorocarbene to Benzotropone Derivatives

Abstract

The dichlorocarbene addition to various di- and trimethoxynaphthalenes has been investigated systematically. It has been found that the carbene addition is oriented by the 1-methoxyl group to the 3,4-double bond and by the 2-methoxyl group to the 1,2-double bond of naphthalene nucleus, and that the spontaneous cyclopropane ring-opening of the intermediate carbene-adducts leads to the preferencial formation of 2,3-benzotropone over 4,5-benzotropone derivatives. The steric effects by methoxyl group seem not to be significant in either the carbene-addition or ring-opening reaction.

trans,trans,trans-1,4-Dimethoxy-2,3,5,8-tetrabromotetralin

“…The bromination of hydrocarbons is an important process, since it leads to useful intermediates for the synthesis of a large variety of bromoorganic compounds (Hileman, 1993;Chambers & James, 1979;Ruasse, 1993). Methoxynaphthalenes have great synthetic importance, as they can be used in ring-enlargement reactions with halocarbenes to give benzotropone derivatives (Sato et al, 1976) and as precursors for other substituted naphthalene derivatives such as naphthoquinones (Song et al, 2000). Taking into account the weakness of the C-Br bond and the reactivity of the Br atoms attached to the benzene ring, we proposed to perform the substitution of these Br atoms with methoxy groups via a silver-mediated reaction.…”

Synthesis of hexabromo, hydroxy, epoxy, methoxy and nitroxy derivatives of tetralins and naphthalenes

“…Methoxynaphthalenes have great synthetic importance for natural products, 14 for electron donors, 15 the ring-enlargement with halocarbenes to benzotropone derivatives, 16 and precursors for other substituted naphthalene derivatives such as naphthoquinones. 17 Treatment of hexabromide 2 with Ag 2 SO 4 in dried MeOH at room temperature under a nitrogen atmosphere afforded the corresponding dimethyl ether compound 6 with monomethyl ether compound 7 in 50% and 15% yield, respectively (Scheme 1).…”

Cytotoxic and Antiplasmodial Compounds from the Roots of Strophioblachia fimbricalyx

“…An IR absorption band for a conjugated carbonyl group (1616 cm -1 ) and UV absorption bands at 328 and 279 nm were in good agreement with the tropolone incorporated in the skeleton of compound 3. 5 On the basis of these spectroscopic data, the structure of new compound 3 was deduced as 3,6,9-trimethoxyphenanthropolone.…”