The total synthesis of precalciferol, has been effected without the use of photochemical methods. 9a-Chloro-des-AB-cholestan-8-one {5ct-chloro-l p-[(I 8 ) -I ,5-dimethylhexyl]-7a~-methyl-trans-perhydroindan-4-one) (1 ; X = a-CI) t and (1 S)-3-ethynyl-4-methyIcyclohex-3-en-l-ol (2 ; R = H) were combined to give the chlorohydrin (3; X = a-CI), which was transformed, first into the dienyne (4) and then, by semihydrogenation of the acetylene link, into precalciferol, (5). Model experiments, bearing on this and related routes to the pre-vitamin, are described.
LS2 9JT1 -Ethynyl-2-methylcyclohex-l -ene, hitherto obtained only as a mixture with one of its double-bond isomers, is obtained pure by dehydrohalogenation of o-halogenodienes such as 1 -(2-chlorovinyl) -2-methylcyclohexene (6 : X = CI). The optically active 5-hydroxy-2-methylcyclohex-I -enecarbaldehyde (1 0) reacts with chloromethylenetriphenylphosphorane giving mixed cis-and trans-w-chloro-dienes [ c f (1 1 )], dehydrohalogenation of which gives the title compound (1 2). required for the synthesis of precalciferol,.FOR use in the synthesis3 of precalciferol, we required the title compound (l2),f which was destined to provide ring A and carbon atoms 6 and 7 of the previtamin. Experiments on its preparation are now reported.The parent compound 1-ethynyl-2-methylcyclohexl-ene (3) has been prepared several times in the past,4 but always in admixture with one of its double-bond isomers. Thus, by dehydration of the appropriate isomer rac-(1) t of 1-ethynyl-2-methylcyclohexanol with phosphoryl chloride and pyridine, a mixture is obtained containing ca. 75% of the desired compound (3) and 25% of the isomer mc-(2). We have separated these two isomers by preparative g.1.c. The isomer (3), A , , 230 nm. (E 11,500), in its n.m.r. spectrum, showed no vinyl proton signal but singlets corresponding to one ethynyl proton (7 7.0) and three allylic methyl protons ( 7 8-12>. In contrast, the isomer rac-( 2) showed signals for one vinyl proton (7 3.9 multiplet), one ethynyl proton (7 7.33, singlet), and three methyl protons (7 8-85, doublet, J 6.5 Hz).As this method is not suitable for preparing hydroxyderivatives of the enyne (3), other routes which might lead to the homogeneous parent compound were explored. The unconjugated isomer mc-(5) was obtained by treatment of 6-chloro-l-methylcyclohexene rac-(4) with ethynylmagnesium bromide and copper(1) chloride 6 in tetrahydrofuran. Treatment of compound rac-(5) with sodamide in liquid ammonia moved the double bond into conjugation with the ethynyl group, and gave in high yield the enyne (3); it was free (g.1.c.; n.m.r. spectrum) from the starting material. In further experiments of this kind, however, formation of conjugated material was incomplete, although extensive, and although we were later able to repeat the original successful experiment, the conditions necessary could not be defined.t Structural formulae in this paper represent absolute configurations. The prefix YUC denotes a racemate; thus rac-(1) means the racemate corresponding to the structure (1).
SzlmnzaryThe optically active diol (9), obtained from the of precalciferol,. Hitherto, the en-yne (3) has been available3 only as a mixture with one of its double bond isomers; for example, a mixture of the en-ynes (3) and r-(2)I is obtained by dehydration of the tertiary alcohol ~-( l ) .
Description This comprehensive ASTM manual provides detailed guidance for developing and implementing a lead hazard management program. It follows the outline described in ASTM E 2052-99 Standard Guide for Identification and Management of Lead Hazards in Facilities. 17 chapters cover the following fundamentals: • Setting up and administering a lead hazard management program • Designing and implementing an operations and maintenance program • Collecting information on facilities for decision making purposes • Classifying buildings based on their likelihood for lead hazards • Evaluating buildings for lead hazards • Responding to elevated blood lead investigation • Conducting occupant education and awareness programs • Hiring consultants, laboratories, and contractors • Planning and performing lead hazard control activities • Ongoing monitoring and reevaluation of lead hazards • Role of lead hazard programs in real estate transactions.
Standard operating procedures for real estate transactions should be included in the Lead Hazard Management Plan to ensure compliance with regulations and protect future occupants by requiring the full disclosure of known lead hazards and potential lead hazards.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.