Woocommerce, wrap any content in the woocommerce default template of your store.

woocommerce-send-email-using-default-template.php

<?php
/**
* Wrap any content in the WooCommerce default email template of your store, for any use. Get the heading, message and footer to send.
* @author Renan Diaz <reandimo23@gmail.com>  
*/

function wrap_email_content( $heading = null, $message = null ) {

		if ( $message !== null && !empty($message) ) {
			
			// load the mailer class
			$mailer = WC()->mailer(); 
			// create a new email
			$email = new WC_Email();

			$email_heading = ( !empty( $heading ) ) ? $heading : get_option( $this->option_name . '_default_heading' ) ; 
	    $message = do_shortcode( $message );

			// wrap the content with the email template and then add styles
			$output = apply_filters( 'woocommerce_mail_content', $email->style_inline( $mailer->wrap_message( $email_heading, $message ) ) );

			return $output;
		}else{
			return false;
		}

	}
  
  $message = 'Some content <even with shortcodes>';
  $content = wrap_email_content( 'Heading Example', $message );
  // load the mailer class
	$mailer = WC()->mailer();
	//recipients list
	$recipient = array('email1', 'email2');
	//Headers
	$headers = "Content-Type: text/html\r\n";
	//send the email through wordpress
	$mailer->send( $recipient, $subject, $content, $headers );