OTBI prompt set default values for date between first and last day of current year

I know that I can set a default for a prompt as todays date using the SQL expression

select current_date from "Workforce Management - Worker Assignment Real Time"

I think the following formula will convert todays date into the first day of the current year, although the syntax may need to be tweaked:

TRUNC(current_date,'YEAR')

and that a formula like this will get the last day of the year:

TIMESTAMPADD(SQL_TSI_YEAR,1,current_date)-1

I tried combining the expressions but it was not successful. Where am I going wrong? It must be possible to be able to have dynamic date prompts to enable reports to be scheduled.